The only thing I can suggest is making up two plans, yours and his, he may have some good ideas that might enhance the space and your ideas. Remind him that woman do things differently then men, so even though an idea may work well in the workshop, it doesn't do well in the sewing room. Remind him that you realize he is trying to help you and that you appreciate all of the effort, but shouldn't it be a room that works well for you?