I am not a LAQ but if I were, I would want a room on the ground floor in my house that was as large as possible to accommodate built in storage for batting/threads/pantos/marking tools/samples/books and multiple customer projects awaiting quilting/billing and mailing information and files for the business, etc and to trim down quilts afterwards. I would want some natural light. I would not want a separate building but I would want a customer entrance and a small area for them to sit and discuss quilting patterns etc.
I would also want a radio or television in the room.
The best idea would be a set of pocket doors connecting the studio to the rest of your house so the room doesn't feel claustrophobic when you are working.