I would not reccomend this unless you are a trained professional. You might be able to find a professional to even build with you so you have someone on hand that knows what they're doing.
Research is your best bet. Research playground equipment companies and ask for their specs. You can take those specs and build you own equipment. Remember that the equipment needs to be on top of a soft surface!
It's a bit hard to advise you about that because I do not know what kind of handicap he has. I would recommend looking up some DIY videos about playground building and alter whatever won't work with his handicap.
More than likely you can buy the equipment online, and assemble it once you get it. It may require a bit of time consumption but, places like ALLEN VENTURES INC., and AMERICAN SWING PRODUCTS carry these products for you.
