Hi, do you guys know these rooms that apperas on behind the scenes maps (somewhat on bts underground), that there is computers, tables, meeting rooms, etc. What are the textures used for it? and is there any documentation about it? valve developer community says nothing about it

Search for these keywords to get some of the textures: "factory", "bts", "office", "concrete", "observation"
For office models, see props_office/, props_bts/, props_lab/, props_factory/, etc.
Check instances/labs for some observation room instances. Underground maps use totally different textures. You probably want to decompile the sp_a2_bts1 - 6.bsp maps (GLaDOS escape), and sp_a4_finale1-3 (Wheately escape) to see what exact textures were used on ceilings, floors and walls.

thank you. By the way, I accidentaly deleted my instances folder on portal 2. Can you give me your copy? (If you think I have a pirated portal 2 copy just pm me at http://steamcommunity.com/id/RenatoBeSt/ ). Also how do I decompile maps (and thats legal?)

To decompile maps, use BSPSource. It's fine for learning purposes, just don't copy-paste stuff or republish the maps. Try vertifying your game cache, that should restore the original instances.

I already did that but it only restored the p2editor folder on instances

Verify your Portal 2 Authoring Tools cache.

it worked thanks =D