I am not sure of all the factors involved in your pole building, but truss ratings are usually measured in pounds per square foot of area. It does not mean that you can't hang anything that weighs more than 5 pounds from the trusses, if that is what you are thinking. You just need to make sure that you don't hang anything too heavy from a single point without possibly bracing it some to spread the load out. Ceiling fans, regular tube style fluorescent lights etc. would be just fine as they all actually weigh very little. Most garage doors weigh several hundred pounds, but their weight would be spread out over 100 square feet of ceiling or so when the door is in the up position, so even a 500 pound door could be fine with your truss structure. In many ways a garage door can almost be thought of as more of a live load than a dead load, because most garage doors spend very little time in the up position adding weight to the roof structure. Also some of the garage door weight even in the up position transfers to the wall instead of the ceiling if you are planning on having a standard rail type door. If you have space above the top of the garage door opening to run the door vertically for a few feet before it bends and runs along the ceiling that even helps to take more weight off of the roof structure.
Insulation weighs almost nothing, so the blanket comment that you can't insulate is boggling to me. Even if the structure can't handle the weight of sheetrock, you can still possibly lightly insulate and then cover the ceiling in plastic and then really thin plywood (or something else lighter than sheetrock) just for the purpose of creating an air/vapor barrier, to make it all look more finished, and to help hold the insulation in place.
As an extra side note, sheetrock is heavy when you pick up a full sheet and try to carry it, but 5/8 sheetrock is only about 2.3 pounds per square foot of area in actual weight. I would be surprised if sheetrocking and lightly insulating the ceiling with something light like fiberglass or rigid foam would add more than 3 pounds per square foot to the truss' ceiling dead load. You will just have to do some quick calculations based on what your specific roof type is to see what options are available to you.
