raised cornice for rafters

I am in the process of designing a detached garage with apt loft above. Rafters to rest on top of raised cornice (3- 2"x6"'s) on top of ceiling joist for a little extra height because I need all the extra room I can get. My first question is: is this ok, shouldn't go any higher w/ the raised cornice right? The only other option I can think of to get more room without making entire structure wider is to use 10' studs on first floor but have a 9' ceiling w/ jacks supporting joists. Also with first example of using the raised cornice, when drawing living space upstairs (12:12 pitch) I am measuring 1' rise to 1' run measuring from outside wall across floor and from floor to rafters. I figure the 3-2x6's will offset the amount I am losing for rafter notch cut, finished floor and ceiling. Hope all this is making sense and thanks for any help, I can provide more detail if needed.