Need advice on contractor's quote for completed roof and windows

[Crystal Em]

We're working on our first project, a SFH flip in Houston, TX.

Our contractor presented us with a price list tallying the work he's done so far. The two largest items being replacing some windows and reframing the roof of a pre-existing 400 sq. ft. back addition to the house. 

He is quoting $3000 in labor and materials for replacing 10 windows (including one small window over the sink in the kitchen) with standard vinyl replacement windows. 

For the roof work, he is quoting us $8000 in labor and materials for replacing the previous flat roof, reframing it to match the pitch of the rest of the house, and raising the ceiling inside the addition to match the 8' ceiling height of the main house. 

What do you guys think of these prices? They sound like a lot to us, particularly for the roof work since it's only 400 sq. ft., but being newbies we have no frame of reference. Maybe we're actually getting a steal. 

I've added some pictures to give a clearer understanding of the work.