A few things to note:
The building: It is remarkably large, and your still using the default shadows- which doesn't help you very much
So I would suggest creating your own shadows.
To do these shadows you need to use a black brush and set the transparency to around 35-37% depending on your preference
they also need to be created on a seperate layer
which you can label wall shadows. This just makes it look slightly more natural than square boxed in shadows....*shudders*
Another thing you could add is shadows on the floor, due to the fact that it's outside there won't be too much in the centre, but for this you need to get a brush that is around 5-10% transparency, then you can add some shadows beneath the buildings, to and also around the trees.
Personally I wouldn't have such a big building...it also is still "blocky. try creating a brush using the grass from RPG Maker VX or something similar.
Overall, it's a brilliant start and I look forward to seeing more of your maps, the more you create them the easier it gets