For human , can build a box , could be 3bps or change.
With hitpoints. Players can build other structures on top of it .Reators,repeaters,turrets,spawns..etc can build on top of it.
Another box can build on top of a box.
The size of this box is a bit bigger than a turret, about 1 turret can be build on top of 1 box.
dretches can crawl on it, aliens can jump across it if it didn't build too tall, or chomp to destroy the boxes.
ofcourse, if aliens want, there maybe similar structure for aliens.