State side, we have tool rental outfits for this type of need. So look up tool rentals. There are crank type jacks which go rather high but you will need to have an idea how much load you are lifting, in addition to maximum height. You may also need two people and a truck to get the jack to the job site.
how to hold up my roof while the joiner works on it-- what are the jacks called -- how much do they cost -- where do I buy them in uk? -- your help would be greatly apprieciated !!
I know them as pole jacks, they come in different lengths, and are available for rent from scaffolding companies. They cost a couple of hundred each, so are to expensive to buy in quantity for one time use.