I have been meaning to make a transport-cum-flyable heavy fighter thing (alal the millenium Falcon), but never got round to it yet...... ach well, maybe after the exams are done (eep)
As for transports....terran ones should have flat, long edges that meet at an angle IMO. i.e. chunky. 2 key things, I reckon are - a) placing a docking hatch (which is kind of a focal point) and b) deciding if it's atmospheric (which determines where the docking hatch /any doors are, the overall structure, etc).
I'm not sure if I have any decent ones I can show (can only thing of one, which is kind of under wraps).... but there'll be no shortage of examples in other games, that's for sure.