I can't help thinking you'd be joining a long line of redundant builders into this field but if you think you can provide a reliable service, go for it. I work in property management and a good, reliable tradesman is worth his weight in gold. Might be worth getting your name out to the agencies in the area as well as approaching individual households. Bear in mind though, if you're doing this properly you'll need insurance and as soon as you mention you go up ladders, the premium shoots up! Although you can get long handled tools.
Good luck with it.