This is a step by step process for layout and modeling of gable dormers on a pitched roof, suitable for a detailed building model. It takes a lot more words to describe, than it takes time to do! (At least, after you've practiced it a few times...)
This tutorial begins at the point of you having the shell of a building. Exterior walls, and the slabs of the roof have already been modeled. Refer to the cottage tutorial if you are unsure how to get this far.
1. Position and size the dormer by making a simple block to represent the walls of the dormer. In this tutorial we are making a six-foot wide dormer. Be sure to make the block long enough that it extends well into the "attic space" inside the roof slab.
Check this dormer massing block in front and side elevation views, to make sure you have it where you want it.
2. Next, make little roof slabs for the dormer itself, and tilt these up (selecting their inner face with the faces tool, then dragging or nudging the edge face upward). Make the length of the dormer roof pieces short enough that they don't touch the main roof. In this tutorial we are using a 12/12 roof pitch.
3.Then, when they are at the correct pitch, use the
Fit Object > North command to extend the little dormer roof pieces over to the main roof slab.
4. Now, select the dormer massing block, and wallify it (in the Edit menu), setting the appropriate wall thickness.
5. While the walls are still selected, use the
Fit Object > Upward command to fit the walls up into the dormer roof.
6. Use the
Trim tool to slice the extra ear off the front wall of the dormer, where it sticks above the dormer roof after the
Fit Object > Upward operation.
7. The innermost piece of wall from the dormer massing block is just scrap. Select this piece, and delete it (by typing the Delete key (the Backspace key for Windows).
8. Go to a side elevation view, and zoom in so you can see the dormer pieces well. Then select one dormer side wall, and use the Trim tool to slice it along the front surface of the main roof slab. Select and delete the inner scrap piece of that wall. Repeat for the other dormer side wall.
9. The dormer should now be externally complete.