Lots of threads on here about suitable housing, Crazyhorse, and as many opinions as there are members I think. The main thing is to research carefully what are the most important things to look for in a chicken coop and run. Lots of people do convert sheds very satisfactorily and it would be a pity to miss out on their hard-won experience. Maybe if you outlined your plans, others could comment? Have a look at the very long thread 'Building a new run' at the top of this section, for some starting points. It sounds as if your girls will have a lovely lot of space - does the wooden fencing go right round, and how high is it? (remembering that foxes can jump 6ft)