2nd Floor addition-exterior walls/roof trusses first-add interior walls later?

I'm slowing pulling together quotes, materials lists, etc...for a second story addition. I will be serving as the general contractor but also doing a lot of the finish work myself. This will be a simple 24' x 26' box with a gable roof. I was quoted $85 each for the trusses, delivery included, then the crane is billed by the hour. I would like the framing crew to put up only the exterior walls, set the trusses, sheath the roof and walls, lay down the roof (tar paper, ice shield, asphalt shingles), apply house wrap to the walls, and install windows-basically, get the box "dried in." At this point I'd have a 24' x 26' box that's protected from the weather and easily sealed off/insulated from the rest of the house that I can work on as I have time, putting up the interior partition walls to create rooms. Is there a reason not to do it this way other than it will take more time?