I started with using our one spare bedroom. The rooms are small, but it was enough room for me.....in the beginning. It was on the main floor and I didn't sew when DH was home due to the noise. Once I got the longarm I used the den downstairs AND the spare bedroom. Now I have it all down in the den and have made the spare bedroom my office. The den has room for all the quilting stuff and a recliner so DH can join me and spend time.
Whatever size you think will work for you, add at least 5 feet and that will be more like it. A closet to store supplies in. Room for all your fabric, and supplies. Room for a cutting table, your machine(s). A wall to use as your display wall..... etc.
Have fun house hunting!
Phyllis
QuiltingGrannie