Caitlin,
If you are in AC 9 you either have to make three roofs one on top
of the other or buy or make an eave soffit object.
If you are in AC 10 where co-planer tool elements clean-up
with each other you can model your soffit with roofs.
One for the main roof, one for the soffit, and one for soffit shoulder.
Also, it has been suggested that in AC 10, eave soffits can be made
using complex profiles but I don't know if the joint with the main
roof will clean up with the profile.
Peter Devlin