Bridges in Boom

I can make them in zdoom, but can they be made in boom?

Boom does not support over/under, so you can't make object bridges.
Boom obviously does not support 3D floors either. (Neither does ZDoom, but it's always tempting to jump from it to GZDoom.)

There is a way, though. It basically involve cheating by using mid textures (for making the bridge visible) and self-referencing sectors (who are thus invisible) that are instantly raised or lowered to make the bridge walkable: crossing them from "below" lowers them, crossing them from "above" raises them.

It doesn't necessarily work well in multiplayer...

http://www.doomworld.com/tutorials/intro.php