If your 6x4m shed is walking distance from your house, it's a better option than a space three times that size that you have to travel to. If you find more space away from home, use it to store things, and do the active construction as close to home as possible. I have built the majority of my plane so far in spare time at home. I put an hour or two of build time in every day before work. If I had to get in a car to get to the plane, I'd be hundreds of hours behind where I am now.