I've recently written several guides to various aspects of chicken keeping and posted them on my blog. You might find the
Housing one useful when deciding what to do—bear in mind that I'm writing mainly from our experience in north-east Scotland plus a few insights from when I lived in Australia. If anyone is interested in the other guides, there's a
Chickens page that serves as an index.
Also, if converting a shed, bear in mind that in colder areas too much space can be a problem as can too much headroom above the chickens.
When outside temperatures remain below freezing for days at a time, the chickens need to huddle together for warmth. They also need to perch in the warmth at the top of the hut. If there's too much space, chickens roosting on their on can suffer frostbite or freeze to death. If there's too much space above the chickens, they won't be perched in the warmest air.