Tim, if you are using a corner to build a closet(and if the corner is square.)Measure out from the corner the same dimention each way.This will give your new wall an angle of 45 degrees to the existing walls.the closest stud you can get to the existing walls will be tight to the drywall on the inside of the new wall and 3 1/2" away on the outside of the new wall.Rip a stud on a 45degree bevel the full length and nail it to that last stud with the bevel against the existing drywall,a bit of glue will help it hold if no backing is there.Some things are easier to show than explain,hope this helps.Luck