Run the plywood down to the top of the knee wall.
Framing out an attic.
Stand the front wall and align it with the marks on the floor.
Collar ties are horizontal members that like rafter ties extend from rafter to rafter but.
Plumb the corners with a level and brace them with 2x4s.
This is the full view of the attic.
It s got a 2x4 stringer running down the middle of the attic space on the floor as well that i d like to remove in order to have a flat subfloor all the way across.
Shim under the bottom plate to level it if necessary then nail it into the floor joists with 16d nails.
If you want your attic space to have a flat ceiling you ll need to add collar ties to the framing.
The plywood will create a smooth strong ceiling without having to apply drywall tape and mud to the ceiling.