size of steel beams

i am in the process of building a shop and was looking in the granger catalog and found a kit with the trolleys to build a bridge crane. the question i have is what size steel beams would be needed. the kit i was looking at was a 1 ton capacity. the shop will bee 21 feet wide and the bridge beam hung off the two 21 foot beam would be about 13 feet. if any one has a source for the info on sizing the beams i would really appreciate it. thank you in advance travis