I have four hipped dormers to make for the William and Mary dolls' house, and I started with the one in the kitchen roof. I'll do a proper tutorial on hipped dormers when I do the three on the main house, but here's a walk through.
Here's my reference photo:
Based on this photo, I chose the Housework's working casement window. I painted the window white and added the panes using 1/32" vinyl model striping. Then I built my dormer from foam core, because it's light and easy to adjust. I glued and then duct taped the dormer together.
I drew the outline of the dormer unit on the backing, and cut out the opening.
I glued the dormer to the backing panel over the hole, and used narrow strips of aluminium tape (used for duct work) to mimic lead. I slated the dormer with Richard Stacey Versi Slates, using folded slates as ridge tiles. Then I started slating the roof, making sure that the backing panel for the dormer would lift free of the roof base, so I have access to the little room underneath.
I've run out of slates, so have to wait for my shipment, but I'm very pleased with this first attempt!