I have a garage that is just under 19'x20' with gabled ends and 2x4s on 24" centers for ceiling joists spanning the 19 feet. I have some light stuff stored in the attic space, but with about a 6" on 12" roof slope I feel that I am missing out on a lot of storage, which could potentially open up the garage floor for crazy activities like parking our Jeep.

My question is, what size beam could I run longitudinally to carry the load of heavier storage? I assume that 6x6 posts would carry the load at the ends, but should I triple 2x10s or 2x12s? It would be great to have the use of the garage I bought for a workshop and parking, but so far that hasn't panned out.