The first thing you need to do is to figure out how much space you have. A standard ceiling is 9 feet and a floor/ceiling is a foot or a bit more. This means to have a second floor, you need an area with 19 feet of height. Buy a laser level and map out how big the space will be, with at one foot intervals.

Without a good idea of what you're working with, any of our advice is worthless.

Only the flat ceilinged area next to the stairs would appear to have the 7' minimum head height. The dormer would be required to make that into fully usable rooms. That's a big expense, to completely reframe the roof, as is framing and adding the second floor. I bet you could buy a different house with more space, for what that would cost.