Alternately, a detached shop can often be located closer to your property line and offers you a bit more freedom in terms of the type of foundation you can use. It may give you a sense of welcome separation from your home and open up yard space or allow a deck on the back of your house that would otherwise be lost behind your shop. In an urban setting, if you would like to have a wood stove in your shop you may find it more challenging to find an insurance carrier that allows one in an outbuilding. Also, outbuildings can be subject to more stringent height regulations than additions.
Spray gun: Not every woodworking job gets a film finish, but most of mine do. And of those, everyone will meet a spray gun. For a million reasons, including making finishing fast and fun, I recommend using a spray gun whenever possible. It will raise your game and make you n0t hate finishing. (Click here to read my thoughts on purchasing a spray gun).