A knee wall is just the thing to complete an unfinished attic or dormer space. It is easiest to do this kind of project with a nail gun.
You will need to measure carefully and take notes. A scale drawing will not be necessary, but a scratch pad will come in handy for writing down measurements and possibly sketching some of the angles.
You will need a bottom plate, which is just a finished two by four that runs the length of the wall. The plate will have to have short studs, which must be aligned to the existing rafters where you are installing the knee wall. The height of the wall determines the length of the short studs.
After determining the length of the bottom plate, cut it to the proper length. Mark it at each place you are going to nail a stud. The studs will line up with the existing rafters and be nailed to them on an angle.
To figure the studs, measure from the floor up to the height you want the knee wall to be and mark the rafter. Use a level, standing with one end on the floor and the other touching the mark. When the level is plumb mark the floor by the bottom of the level.
The top mark will align with the pointed side of the stud and the bottom will align with the outside bottom corner of the stud.
Now, square cut the stud long enough to sit on the floor plumb and go beside the rafter and above the mark. Make sure it is plumb.
Draw a line on it where it lays against the rafter. When you have it marked cut the slanted end leaving the line. You should be able to see the line on the short stud after you have cut the angle.
Square cut one and one half inches off the other end. The short studs will be pointed on one end and square on the other.
All of your short studs will be the same size. Use this one as a model to make all you need.
Nail all the square bottoms to the plate, then move the plate into place. Plumb the studs on each end and tack the tops to the rafters and the bottom plate to the floor.
Recheck for plumb and proper placement. When you are sure everything is right nail the plate first and then all the studs permanently.
If you are going to install drywall, you may need to add extra blocking as needed. Blocking is short two by fours nailed between rafters and studs.
Be sure to insulate and do any wiring before adding the drywall.
Your knee wall will make the room more useful and will give it a nice finished look. It is a great place to install speakers and add extra storage.