what do you mean, randomly selected?
Sometimes you’ll play on someone else’s dreadnought, so it might actually be a good idea to make the worst possible dreadnought build just for that occasion.
Anyhow, since your question is an excuse to write way too much about dreadnoughts, here’s a nicely divided overview of what dreadnoughts are, the differences between them, and the modules available to be built.
Overview :
Dreads are a gamemode fought essentially exclusively between corporations for control of sectors, which give rewards each day. There is a minimum of four and maximum of eight players per organized wing, although it is possible to queue solo for a random dreadnought fight. Dreads tend to carry an air of competitive play, although there are certainly a number of corps that are less competitive than others.
In an actual game, the top bar summarizes the game state very succinctly. An picture I’m lifting straight off of the NASA forums that was originally made by Mecron:

No, I don’t feel particularly bad about giving other people the information in the picture, since it’s incredibly obvious once you start playing.
Not pointed out: Coloured circles above the dreadnought indicating turrets in that spot, bomb and torpedo indicators (not shown).
There are two win conditions: Timeout with more fleet points than the enemy, or reduce enemy fleet points to zero. Obviously, fleet points are important. They are lost through a variety of methods.
Drones dying will take one fleet point each.
Turrets destruction will take three fleet points each.
Other structures will take 10.
Player deaths will take 15.
Main caliber damage will do about 1 per 10k damage.
Dread torpedoes will do up to 50 points of damage, depending on shield level prior to hit.
Due to the sheer ridiculous damage output of dreadnought torpedoes, I suggest not participating in dreadnoughts until the torpedo launcher is built. Each team typically has a designated Empire LRF to snipe the torps, since they are both small and fast. Due to the importance of the LRF, one also typically invests in an engineer with eclipse launcher to heal it. Other ships all have their own roles in dread battles, typically rather obvious when considering the ship.
Important notes: Drones are actually very tanky, hard-hitting bots in faction-relevant ships. Once turrets are built on your dreadnought, it is typically better to leave any that get through your defenses to them, rather than taking them head-on. The engine trails of dreadnoughts will instantly kill you should you go into them. The white lasers (main caliber fire) will do the same if you’re in the line of fire. The smaller calibers will simply do an amount of white damage should you get in their way. The dreadnoughts are constantly moving forward, although this is easier understood as the players constantly moving aft. There are asteroids in the midfield which will move aft faster than you drift. They can be destroyed by main calibers, which looks wicked cool. Should they not be destroyed, they will typically do severe damage, if not instantly kill, most craft that bump into them.
Dreadnoughts :
The “standard” dreadnought starts with 2000 fleet points, 500k shields, 9k shield regen, and 13.95k main caliber dps. It comes with no turrets, no torpedo launcher, and no bomb rack, although it does come with a standard command tower, shield emitter, and weapon cooler.
Note that any suggested playstyles are my own personal thoughts on the matter, and are obviously not set in stone.
Jericho:
The Jericho dreadnought looks like an Empire dread with oars attached. Unfortunately not very distinctive, but still fairly different from the Empire dreadnought.
It has a shield volume and regeneration bonus over the “standard” dread, taking less fleet point damage over time. Destructible structures are grouped, making life easier for the enemy. The spawn point is at the forward section of the dreadnought, and the dreadnought itself is quite long, making it quite a trek to get from one end to the other.
Strangely enough, the defensive bonus suits itself to an offensive playstyle, encouraging players to stay in the midfield and coordinate pushes to the enemy dreadnought rather than have to deal with the travel time around their own. The bonus to damage tank lends a few more fleet points over time to help mitigate failed pushes. I still don’t have hard numbers for the Jericho dreadnought, and as such can’t say for certain if it’s actually much better or worse than the other two. For certain, though, the folks who use it tend to have a hard time holding their own.
Federation:
The Federation dreadnought is small and aerodynamic (space-o-dynamic, I guess :P), very easily identified at the start of the match.
It has a 200 fleet point bonus and (very) slightly stronger drones over the “standard” dread, adding on a significant amount of tank and an early game advantage. Destructible structures are still grouped, although a good number are out of sight, making life meh for the enemy on this front. The spawn point is in the midsection, away from the enemy dreadnought, and the dread itself is rather small, making it a relatively fast trip to whatever section of the dreadnought one wishes to be.
The bonus tank suits itself to whatever playstyle one wishes. A defensive play can be rather successful, with extra fleet points to burn through while waiting for the enemy team. An offensive play can also be rather successful, with a large number of extra fleet points to mitigate failed pushes.
Empire:
The Empire dreadnought is blocky and rectangular, visually somewhat similar to the Jericho dreadnought.
It has a main caliber damage bonus over the “standard” dreadnought, dealing more fleet point damage over time. Destructible structures are far apart, making life a little more difficult for the enemy team. The spawn point is at th eforward section of the dreadnought, although closer to the midsection than Jericho’s, making it still somewhat hard to get to where one wishes to go.
Oddly enough, the offensive bonus suits itself to a defensive playstyle, as the dreadnought will do more damage to the enemy over time, but provides no extra support should a push fail.
Modules :
There are a total of nine module slots on each dreadnought. Three passive slots, four turret slots, and two structure slots.
Passive Modules:
The passive modules include the command, shield, and weapon modules. They are highlighted on the map, and are featured on the game summary bar at the top. Each can be captured like a beacon, or have a bomb planted in it. Capture rate is about the same as in capture the beacons. Bombs will take 50% of the capture points off of where it was planted, and do extra fleet point damage besides. Any capture points lost cannot be regained through any means.
Command modules:
Currently, the only available module for the command slot is the command tower. Normally provides faction-specific drones every minute or so. Once capped, drones stop spawning (although ones already out behave exactly the same as before), and 200 fleet point damage is done to the dreadnought. Upgrading reduces this to 150 fleet points.
Shield modules:
There are currently three shield modules available.
The default shield emitter increases dreadnought shield regeneration by 6k points per second. Upgrading increases this to 6.6k. This happens to be the best module for all circumstances.
The shield emitter catalyst gives a 360 fleet point bonus at the beginning of the game. Upgrading increases this to 396. While it has superior early-game performance, it has a break-even point with the shield emitter at 10 minutes. Should the game be won afterwards, you would have done better with the shield emitter. Should the game be lost afterwards, you can blame the module. Should the game be won before, it was clearly unused. And should the game be lost before, you clearly got stomped pretty hard.
The resistive coating emitter will hard counter an enemy weapon booster, and give a 7% chance to fully block any incoming damage. It has sub-par performance relative to the shield emitter, but will still manage to outperform the shield emitter catalyst around the 15 minute mark. Considering the dearth of weapon boosters in use, this module typically doesn’t fare too well.
Weapon modules:
There are currently two weapon modules available.
The default weapon cooler increases dreadnought damage by 37%. Upgrading increases this to 40%. This happens to be the best module in most circumstances.
The weapon booster increases main caliber fleet point damage by 50%. While this is a great bonus, it is typically stopped by the fact that default shield regen (with shield emitter) is larger than default main caliber damage (without weapon cooler).
Turrets:
Turrets are automated dreadnought defense weapons. While expensive, they very effectively avert attackers and destroy drones. Each bought “turret” can only be used in a single spot – meaning, buying the second slot plasma turret gets you a second slot plasma turret and no more. However, in-game, each “turret” gives multiple turrets arranged in a band around the dreadnought for maximum coverage. There are currently two kinds of turrets.
Plasma turrets deal EM damage. They have a respectable rate of fire and significant damage, as well as high projectile speed. This all comes at the cost of some DPS.
Missile turrets deal thermal damage. They have a low rate of fire and huge damage, but low projectile speed. In return, they get a slightly larger DPS – just remember that a missed shot deals no damage.
Structures:
There are two structure slots on the dreadnought. Each can only take one module right now.
The bomb rack provides bombs after two minutes of there being no bomb on the rack. The bomb is similar to the one in detonation, except it does not apply a slow-down, and detonates for a good deal of damage after being dropped. The main purpose of bombs is to be planted in enemy capture points, taking off 50% of the capture points and dealing a good amount of fleet point damage (depends on which point was bombed). On explosion, whether that be dropping or planting, the bomb deals a high amount of thermal damage to any nearby players.
The torpedo launcher shoots two torpedoes every minute, plus or minus a random number of seconds. Torpedoes will show up on the launcher for a few seconds before launch, vulnerable to explosive damage only. They launch to one of three sites on the enemy dreadnought – fore, middle, or aft. They have a very, very small hitbox and travel at about 350 m/s. Upon hitting the enemy dreadnought, up to 50 fleet point damage is done, depending on enemy shields before the hit. On detonation, should that be from being hit or hitting something, they deal a large amount of thermal damage in a very large radius. A designated Empire LRF is all but required to win against an opponent with a torpedo launcher.