Well, maybe one of this tutorials can help?
Create a random town
[Award Winner] A medieval town map tutorial in Photoshop
[Award Winner] Thatching for dummies...
[Award Winner] Clustered houses for a city in Photoshop
[Award Winner] Eneini: a medieval city tutorial (in Photoshop)
I think all of them are for Photoshop, but I didn't check them all
(I did a search in the tutorial section of this forum on "building")