When you side a dollhouse, you are left with rough looking edges at every corner. You have to hide these with trim. Not all dollhouses will come with trim for your corners. In fact, if the kit does not include siding, you will most likely not get corner trim.
So if you decide to side, you will need to buy your own trim. I buy inexpensive balsa wood strips at the craft store and make my own L shaped trim to fit over corners. It's very cost effective considering that miniature lumber is priced pretty high at miniature stores.
The dormers need a lot of work on the exterior to make them look right. You need to spackle all of the gaps and paint everything correctly. I use a very fine tip brush for the details.