I'd probably use two inch box tubing or two inch pipe, prefer pipe for this, never know what I might lift. Make sure I beam above is secure. Make a roller bracket to fit beam and can roll length of beam.I think 1olbull's jack method will work for not a lot of money. I think I'll use the front wheel lift in conjunction with that just to add stability. I'm paranoid about something shifting, the bike losing balance and falling off the lift. That'd be a nightmare. I had a lift a lot like the one in 1olbull's pic. Gave it to a friend because I had for 10 years and never used it. I'm sure he'll let me borrow it back.
Anyway, I thought about making a lift beam. I see buying them is expensive as hell. What kid of stock would you use? I feel like 1nch and a half square tube would be strong enough.