While looking for why the turret model was broken in GTKRadiant, I stumbled across some info that might help mapmakers out - the hitbox sizes for structures. Here goes:
HumansTelenode: 80x80x8
Armory: 80x80x83
Defcomp: 70x70x60
Medpad: 70x70x14
Turret: 50x50x40
Reactor: 100x100x110
Repeater: 30x30x40
Tesla: 44x44x80
AliensEgg: 30x30x30
Acid tube: 70x70x51
Barricade: 70x70x75
Booster: 56x56x18
Hovel: 100x100x40
Overmind: 90x90x110
Trapper: 30x30x30
Those are all the ones you can put into a map with GTKRadiant. I don't know how big the hive's hitbox is.
PS. I might consider making prefabs with an invisible hitbox brush in the right place, so you can the delete them aftet you've got it in the right place.
Enjoy
