There are basically three ways to get roof trusses for a shed. You can buy a kit, which comes with trusses, either assembled or cut with all the elements ready to be put together. You can buy prefabricated trusses from a building supply or roofing store, ordered to the pitch and size of the shed roof. Or you can make your own trusses, building them on site to the specific size and style you want. The finished trusses are likely to be much alike and installation will be the same.
Design the truss, which is a pair of rafters with internal bracing and joints secured with special fasteners called gussets. Decide on a pitch, the angle of slope, and whether to use a ridge board at the top or form a peak with the trusses. Pick a style and location for internal bracing, which will depend on how much height is needed inside the shed. Most shed trusses will be low pitch, like 4/12, sloping 4 inches per foot of run, the distance between the wall and peak, and will be made without a ridge board, relying on roof sheathing to tie them together.
Use a framing square to mark the rafters, with the pitch angle and rafter run to determine the top cut, where the rafters meet, and the notch that fits over the cap board on the wall. Cut the rafters to size with a circular saw. Prepare the gussets; use either purchased metal plates or triangular pieces of oriented strand board (OSB) sheathing cut to the angles of the rafter tops. Fit gussets along the rafter angles and across the rafters to fasten them. Secure gussets with either framing nails and a hammer or screws and a screw gun (which is stronger).
Assemble the trusses on a level surface, like a driveway. Lay down a pair of rafters, with ends meeting, and fasten with a top gusset. Add a cross tie, a 2-inch by 4-inch board that goes between the rafters at a selected height, ends cut to match the rafter angles. Put the cross tie near the bottom of the rafters if inside space is not a consideration or if some storage is desired in the roof area. Place the tie about halfway up the rafter for more internal space. Build all trusses the same (a 10-foot shed will require only 5 trusses, spaced 24 inches apart). Secure the tie with gussets on both rafters.
Install the trusses by lifting them upside down to the roof, where workers can raise them and nail them in place to the outside wall caps. Use a level to plumb the rafters before nailing. Start at one end and work to the other, plumbing each rafter as you go. Add studs on the end rafters between the cross tie and the wall cap. Cover the trusses with OSB sheathing nailed to each rafter at about 12-inch intervals.
The best way to lift trusses is to position one worker on each side of the roof with a lifting board, a 2-inch by 4-inch board notched to fit the end of the truss. Walk the truss down the shed into position for the roof workers to set it upright and nail it.