Question: I'm making a game with target (orbit camera). I want to limit camera movements when in room. So that camera don't go through walls when moving around target and along the ground.
What are common approaches? Any good links with tutorials? I use Unity3D, nevertheless I'm good with a general solution to the problem

Answer: 
Make a snake game with it. Make a shooter game with it. Make some simple well known games to start off. Once you've done this, you should be more confident with your engine, and making these games will give you ideas on where to keep going.
This is one of the classic problems of game engine development - your engine most probably is too generic.

Pick your favorite genre, perhaps even your favorite game - and look at how things work there. Try to copy a thing or two. Make something good, make something bad. Create experiments and problems. Experiments are useful for finding a good direction to take, an unexplored path. Problems have a tendency to keep developers interested for a long time. Pick something you've never done before to make space for both.