I like to install the center truss after the end trusses have been installed & then work out from there. The roof trusses are going to be 2’ on center & there will be a total of 11 trusses.
The length of the roof is the size of a sheet of paper so fold the paper in half & mark the middle with a pencil. When you lay the roof upside down on the sheet of paper you will know exactly where the center of the roof is. Using your scale ruler the center truss is at the 10’ spot, mark your paper every 2’ this will be the placement of your trusses. Do not start marking using the edge of your paper, either start from the center mark & work out or with the roof still laying on the paper mark from the end rafters.
Do the same thing on the other side of the paper & then cut it in half the length of the paper & tape it to the roof with the lines showing at the very edge of the roof. Now you have reference points on both sides of the roof for installing your trusses & remember these reference points are for the center of each truss.
You now can line up your center truss perfectly on both sides using the center mark on the paper. Glue your center truss into place & clamp it to hold it down until the glue dries. By gluing the center truss at this time it will help with any bowing that you may have in your hardboard roof, it should make everything nice and straight.