Cutting a complex piece of drywall takes a bit of precision and may best be done with a paper or cardboard template. By taping something more flexible then drywall over the space to be covered and marking the dimensions on that, your fit will be more exact.
Ceilings and slants (like attic ceiling-walls) pose a serious problem in the form of gravity. More than one person will be needed to support each drywall panel as it is secured into place. Or you can use a 2" x 4" "T" (cut to the height of your ceiling less 3/4 of an inch, with a 3 foot section of 1" x 4" attached to it as a support.
Drywall screws used with a drywall screw gun are more efficient and convergent here. The pattern for fastening with screws is the same as when using nails - every six inches around the edges and 12 inches in the field. Check codes.
Remember that ceiling pieces should always be installed before wall boards. The wall boards will then serve as added support for the ceiling boards. Angled ceilings may be installed after the walls.
Curves and Odd Spaces
The easiest way to transfer the exact measurement from the stud system to the drywall is with a paper or cardboard template.
Tape the paper to the stud and use a chalk line snapped down the center of each stud to mark the proper measurements on the paper. Transfer these measurements to the drywall. Cut small triangular slits in the paper and tape over these to the drywall with masking tape.
To compensate for the angle being created, cut the template pieces slightly smaller (cut to the inside of the chalk line) than the actual space defined by the studs.
Use the utility knife to make long cuts and a keyhole saw for the cross cuts.
Fasten the drywall to the studs. In these areas, beveled factory edges are not needed between adjoining pieces.