First try at dungeoneering with GIMP

[coredump]

So I am running a roll20 campaign and want to provide some custom dungeons/castles... The problem is that I don't know how to gimp good, so I spent the last few days reading tutorials.

This was my first try at a keep's ground level:


Not pretty, but not too terrible. Just... not the style I am aiming for (Also, can't seem to find good objects that match the style).

So I tried a second thing:



This is more inspired on what I saw from http://www.cartographersguild.com/building-structure-mapping/28015-tower-keep.html]this and http://www.cartographersguild.com/tutorials-how/16160-%5Baward-winner%5D-photoshop-using-paths-create-textured-walls-why-i-hate-bevels.html]this.

One thing I would love to get some help/input is how to make my walls thinner. I used 1 square walls inside but it doesn't look too hot, but I can't think on a way to do it with just a line without losing internal space on the rooms.

I tried this, but still losing internal space and feels weird with the grid:



Also, any other tip is welcome. As you can see, I don't know how to do DOORS yet Or how to actually put symbols for stairs and etc.