i agree with reminding him that this is your space, not his. the rhythm of sewing and design is a far cry from the wood shop or the garage. if things do get out of control, you could offer to go and "fix" his mancave to your liking, so it would work better for "you". mostly--just keep at it. his ideas may make sense if you guys can talk them through. my hubster is retired, too, and until his parkinson's slowed him down, he "fixed" everything in the place until i threatened to make him go live in his little motorhome. he has now recruited a young friend to be his hands, and the one thing i have emphasized is to let me know what you are doing, and where you are doing it. otherwise, i will get the broom, and ride it as only i can! communication is still foremost. that, and "don't cost me another cupboard or storage space for your "improvement"!!!"