No idea where you live so not sure of the urgency if weather is a factor to completing your sewing room. But it certainly would not hurt to get an estimate or two to what it would cost to have someone come in to do it. (It may be cheaper than you think.) Also, you said it was full of "junk." What kind of junk? Junk that would make a good yard sale? Or junk there is no way you can get rid of it and may be appropriate to rent a storage unit. So you may want to get an estimate of a local storage unit close by or maybe invest in one of those little storage sheds to have in the back yard.
My husband was never very supportive of my sewing, crocheting, etc hobbies until I asked him what he wanted me to do. Was I suppose to sit still and just watch TV with him? I need to keep busy. If I am watching TV, usually I have clothes washing, dishes washing, sewing something or on my computer. Just sitting is very hard on me. He cannot understand that I can watch TV and read a book.
They have different ideas what we need and enjoy. Some men are extremely supportive, others just shake their heads. We have been married 38 years and when my eldest moved into her own home I took over the room as my sewing room. He has the front room for his drum room. You just find a happy medium.