Looking good so far - that central buiding certainly helps to fill out the map and I actually rather like the entrance mound.

For the central building it currently looks like it's a cylindrical roof that's top lit - if you want a peaked roof you probably want to darken the right hand side (all of it) and lighten the left hand side. To do this, just create an overlay layer and use the rectangular selection tool to fill the left hand side with white and the right hand side with black. Mask it off so it only affect the roof. That will be consistent with your other shadows too.