I want to build a enderman farm and wanted to use slabs. But I saw a video where he said that they can spawn on slabs, carpets, stairs.... I lokked up in another video that you can use glas and leaves but it wont look good. I tried to look on the Minecraft wiki but it just said that they spawn on solid blocks. Please help me. Thank you!
Like most mobs they'd be able to spawn on slabs in the top half of a block space but not the bottom, I'm pretty sure nothing will spawn on stairs unless they are upside down, I don't think mobs spawn on carpets or glass and probably only jungle animals spawn on leaves.
However, with endermen you have to worry about where they can teleport as well and I'm pretty sure that's almost anything they can stand on.
The normal way to keep endermen from teleporting (and it stops spawning as well) is to either cover the area with water or make the roof 2 blocks high, I think 2.5 works as well.