Trusses are pre engineered and you order them from any lumber yard. Tell them your span and pitch and have them deliveredto your site. You will need alot of friends to help you lift them into place.
2/4's or 2x6's are way to small to carry the 22 foot span for loading purposes. If you insist on that size for design purposes, you are going to need an intermediate support to cut the span in half for light loading on 2x6's (I won't even mention the other size).