Sorry gotta pipe in on the topic:
TGI is not Tongue and Groove I - Beam. Though that is a good one! TGI is just the bad pronounciation of TJI, though the Tongue and Groove kinda makes sense.
Was in the Engineered wood business for a lot of years and even helped design the joists and the machines that produced your roof rafters.
The correct term is TJI (Truss Joist I - Joist), though that is like calling a bandage a Band-Aid. Just the common usage is all, as Truss Joist pretty much invented the engineered wood I-joist.
Those rafters are actually NJ12's produced by the now defunct Nascor Inc., at least I hope they are at least NJ12's (11 7/8" depth). I can only guess why you got them at a good deal.
Sorry, way off topic. Garage looks good though.