Building this house I have had to lift many things that were either heavy or bulky (or both). I knew I needed a electric winch or a good block and tackle to help out. All the blocks I've seen for sale were usually 4 wheel models and awfully expensive. Since I wanted the extra mechanical advantage a 6 wheel model would provide, I decided to build one.
So, it's off to the scrap metal yard to find 1/8" flat steel plate. The side pieces are roughly 3" x 6". All the hardware is 1/2" diameter. Locknuts were used to prevent things from coming apart at inopportune moments. The rope is 3/8" poly, rated for (I think) about 175 lbs. At first I thought 100 ft of rope would be sufficient, I have since added another 25'. The pulleys are 2.5" diameter and came from the local welding supply house; they are rated for 700 lbs.
This thing paid for itself the first time I used it. It has been used a lot to lift and move, particularly in lifting and moving those 20 ft tall A-frame scaffold supports used to side and paint the house. Once, I even used it to straighten out a bowed 2x6 wall stud.
Realize, this was not designed by a professional. It has not been tested, so I have no idea what it's load capacity is. Build and use one at your own risk. If you do build one, don't ever stand under a suspended load. Be careful.