Just moved house and one of the main selling points for me was that it has a decent sized workshop. The main selling point I would think lol. Why is it Women always look at kitchens & bathrooms when they know full well they will get you to rip it all out & fit a new one anyway lol

As well as the walls you need to consider the roof & what if anything your going to do about that, if you intend to do anything to try & keep it a bit warmer or intend to install any type of heating then this is the sort of thing I would be looking at doing before I started to plan where everything was going. Get the basic shell sorted first & then take it from there.