First, let's define a few terms. A king stud, is a full length stud, usually 92 1/4", that forms the outer part of the frame for a door or window. A jack stud, which I call a trimmer, is a shorter stud that supports the header above a door or window. A cripple is a short stud between the header and the top plate, or under a window between the bottom plate and the sill.

The header transfers the vertical load above a window or door opening to the trimmers. In your situation the load may not be significant since the shed is most likely single story. The 2006 International Residential Code, in Table R502.5(1), says that the maximum span for a header consisting of two 2x4s (or one 4x4) is 3' 6"; for two 2x6s (or one 4x6) it is 5' 5"; and for two 2x8s (or one 4x8) it is 6' 10". In your case with a 6 foot door, you should use a 4x8 header.

The rough opening for doors is generally 2 inches wider and 2 inches taller than the nominal door size. Thus if you have a 2668 door, meaning the width is 2' 6" and the height is 6' 8", the rough opening should be 32" wide by 82" high. That means you will cut the trimmers to 80 1/2". Furthermore, the header is 3" longer than the rough opening to allow for a trimmer on each end. In this case for a 2668 door, you'll need a 4x4 header 35" long.

To assemble the door frame, nail each 80 1/2" trimmer to a 92 1/4" king stud using a 16 penny nail every two feet. Then nail the 35" 4x4 on top of the trimmer, using four 16 penny nails on each end driven through the king stud. When you nail the frame to the 2x4 bottom plate and cut out the bottom plate for the door, the rough opening will be 32" by 82". Finish the frame by cutting 8 1/4" cripples to fit between the header and the top plate.

You propose to have a 6 foot door. I assume you mean a pair of 3068 doors. The rough opening is 74 inches wide by 82 inches high. As mentioned above, you'll need a 4x8 header cut to 77" long. As before, the trimmers are 80 1/2" long. The header is nailed to the king studs with eight 16 penny nails on each end.

Windows are framed similarly to doors, except that the space below the window is filled with a sill and cripples. Unlike doors, though, the rough opening for a window is usually the same as the nominal window size. The rough opening for a 4030 window is therefore 48 inches wide by 36 inches high. The trimmers are 80 1/2", the same as for doors. The header for a 4030 window is a 51 inch 4x6. The cripples under the window are 43" long.

Each window should be checked for the correct rough opening. Some manufacturers deviate from the nominal window dimensions.

The window frame is assembled by nailing the 80 1/2" trimmers to the 92 1/4" king studs, then nailing a 43" cripple to each trimmer. The 4x6 header is nailed in place with six 16 penny nails on each end. Now a 48" sill is nailed to the tops of the 43" cripples. Several more cripples are nailed to the sill and the header so that there is a stud every 16 inches.

Actually, the entire wall should be framed so that a stud, trimmer or cripple falls on 16" centers. This may require an extra stud or two, but is necessary for nailing plywood or T1-11 siding to the wall. The nailing schedule is often every 6" on the edges, and every 12" in the field (center). 8 penny galvanized nails should be used.