A bay is quite a difficult project for a non-framer. You have to decide how to support it, which is fairly easy if the floor joist run toward the window (you can just kind of slap a longer piece on the joist and canilever the thing). If the joists run the other way, you have to either remodel the floor, or put the bay on some other supports, like brackets. Then walls, then figure out your roof lines, which is not terribly easy.
It's a significant "small" reno. If things were set up correctly, I would look to do most of the framing in about a day, and there would be a few fairly major repair issues after that - like, new flooring in the bay or the whole room, drywall repairs, and all the windows, siding etc.
It's not the most difficult home reno to do, but it is not insignificant.