I think shadow got it right, the AI needs lots of money to function properly (or have the ship class set much lower) the general AI build order is as follows build a fighter factory and destroyer yard, then at least 5 fighters from the fighter yards, and then the largest ship it can afford from the destroyer yard, if it can't build anything it will try to pump out miners to go get resources and strip the map, in reinforcements it simply builds five fighters, then builds the biggest ship it can until it can't pay for any more or hits the unit cap and then goes the next size class down.