I'm going to close in part of my large garage for a woodworking workshop & lower the ceiling for some limited storage. Dimensions are: 28'10" L x 20' W. I was considering wooden I-joists for the width and wanted to know what construction of these would be needed (if I build them myself) for strength spanning the full 20 ft. The ceiling will be closed in and fulling insulated; with fluorescent light fixtures and only about 1/2 of the area above the ceiling would be used for storage. I was contemplating connecting the ends of the I-joists to a header plate around the outside at either 16" O.C. or 24" O.C. (This is to eliminate the need for lining up directly with wall studs). My concern there, is if I use 24" O.C. will I have to put support braces between them to keep them from racking? So, for a 20' span do I need the equivalent of a 2x12 or 2x10 or ???. If I build them myself, are 2x3's okay for both sides of the laminate or is that too much?