You are most free to ask for anything. It helps me spend my time making tutorials that will actually be useful to folks which is much more fun and productive. I make no guarantees I'm capable of giving useful help on some subjects though (bogie should do one on placing items in rooms, his clutter work is superior). For trees there is always insertable map elements (those pre made or pre rendered ones you can find on many sites), or using a combination of a texture and hand drawing your light and shadows to give it depth and interest, but my standard technique is shrubs. For really big trees sometimes its more appropriate to to just do the bases, the trunk that is, as the upper part of the tree isn't down were it can get in the way of an encounter. When you say interiors do you mean the interiors of buildings? Give me an example and I might be able to tailor my help towards it.