Playhouse North Wall

I'm finally moving on to building the north wall of the playhouse!  I've been debating how to manage the assembly of the four walls and when to raise them up.  I decided to move the east wall frame off of the foundation, and I parked it leaning against the side of our house because we have limited floor space.

Now I am building the north wall frame on the foundation.

Then I will build the south wall foundation.  But where should I do that?  If I build the north wall on the floor, it will be hard to install screws around the edges of the frame.  So I might just build the south wall on top of the finished north wall while it is still lying flat on the foundation!  I think that should work.