Setting roof trusses is no walk in the park, but if you have already built the trusses and they simply need to be set, you have already completed what most people find to be the hardest part. The most important thing when setting trusses is accuracy. If the trusses are not placed in the right positions, there will be serious problems with the shape and function of the roof.
Set the trusses into place. This job requires at least two people. The first of the trusses should be set against the wall of the building. The trusses should be upside down so that when they are lifted it can be turned into place. Stack all of the trusses in a similar manner.
Walk the trusses into position on the ground one at a time. Start on one side of the structure and spread the trusses out to each area of the home or building so that they can be raised into place, without needing to be moved on the roof.
Brace the second gable end on the roof and plumb it. Do not brace all of the trusses this way. Rather, it is better to have a few 3 m (10 foot) pieces of 2.5 x 10 cm (1 x 4 inch) boards that can be used as braces.
Mark each of these boards with a pen or pencil exactly 60 cm (24 inches) from the bottom end of the board.
With one person on top of the roof and the other at the bottom with the trusses, lift the first truss up into place. Once a few of the trusses have been lifted, nail the ending part of the brace over the second gable end truss at the top of the roof.
Line up the other trusses with the 60 cm (24 inch) marks you made on them to set accurate spacing between the trusses. In addition to making the proper spacing, this also will help all of he other trusses to properly be put into place.
If the second gable end truss does not line up 60 cm (24 inchesO) from the centre of the neighbouring truss, measure the distance between these trusses on the cap plate and move the mark on the brace to match the distance.
Not using a ruler or measuring tape to make your measurements will almost absolutely result in a crooked roof.