Unless I'm not seeing something in the photo, I think a good solution would be to construct just 2 new gable roof extensions, at right angles to the existing center gable. Shorter one on the left, longer one on the right. I'd frame it using individual rafters and 2 ridge beams, such that the only penetrations necessary in the flat roofs would be where each rafter ties into its support wall. One person could do this by himself, quite leisurely, and it would probably be a darn sight cheaper than buying trusses, and renting the crane to set them in place.
I did a very similar major roof remodel on a large house in NM, with a slightly more complex roof to tie into, and it worked out extremely well. I decided to do it myself after having 2 roofing contractors/framers come out to give me their estimates to do the job--first one said it was at least $15,000 (this was in 1992!), and the second said it couldn't be done, and refused to bid it. I did it for a total of less than $2200 in materials (not including shingles) and less than 2 weeks of my time. Framed the new roof at a 4:12 pitch, and used all Doug fir 2 x 8 rafters, most of which were 22 feet long.