Yeah, almost any of the wall textures (wood, metal, block, brick) can be used for spawn rooms inside buildings and then you also could have a spawn room inside cliffs and used displacements. There are many things you could do. I would just take a look at some other maps and get some ideas.
Some ideas though for spawn rooms would be..........
Computer Supply Room
Maintenance Room
Warehouse/Storage
Garage
Farm House
Cave/Mineshaft
Lumber Yard
............and that's just naming only a few standards. You could really do almost anything.