I'm mostly winging it, but I have the rough plans put toghether already. I'll build a 4' by 8' frame out of 2x4's, put a 1/2" plywood deck on it, then probably another round of 2x4's around the top as a "spill guard". At each corner, I'll install a lag hook and attach a single pulley, with a matching lag hook and pulley mounted to the ceiling. Then I'll "lace" a rope from the floor up through each of the pulleys and ultimately lag the end to the platform. Once everything is laced together, I will hoist the system up and tie it off to another lag hook by the door.
parts list:
5 - 2x4 studs
1 - 4x8 sheet of plywood
7 - pulleys
8 - lag hooks
1 - lag hoop
100lf - 3/8" nylon rope
The pulleys I bought at home depot last night are rated for 125lbs so when you consider there will be 4 connection points on the roof, I estimate this will hold a payload of about 400lbs (once you subtract the weight of the platform and add a factor of safety). Also, because this will work as a series of pulleys and I have no intention of getting anywhere close to the full weight limit, I *shouldn't* need any help hoisting this up.
I'll post pics when I get this put together.