I decided to only put a 4' loft at one end and 2' at the other. In reality, 4' at both ends made the shed feel too closed in. I used doubled-up and glued 12' 2x4's with blocking in between. Both my son and I stood on it while we were putting roof on, and there was no flex.
I decided to make the sides decks 15" deep. All the studs in the shed are 7' tall, cut from standard 8' boards. We had a big pile of 12" pieces, so I used those for the blocking. The OSB is glued and nailed every 6" along these, creating wall stiffeners, as well as storage.
Here is another dark picture (on purpose) showing the vent holes in the soffit blocking. I used left over pieces of the OSB siding, drilled 5 holes in each, and stapled window screen to the backs. This cost $6 for the screen instead of about $50 for the pre-made vents.
My son and I got the OSB sheeting on the roof and nailed down. I will cut the excess off with a skill-saw tomorrow. Once done, I need to screw the OSB to the rake and fascia boards - I don't like to nail these, since they can easily come loose.
Hopefully tomorrow I will get most of the siding details done...