First dungeon of mine - Problem with objects

[Kikouk]

Here is my first map of a dungeon i'll use for a first D&D scenario, that's almost what I wanted, but I'm still looking how to include some elements, like tables, beds, etc. on this map. I work with PS...

When I try to define such objects as brushes, it is just terrible, because it's pixelisated, a little transparent, and it loose all it's color and so it's interest (for example, a table became juste a black square despite of a quite good looking wooden brown table...)... How can I do to include some elements easilly?