How high is your deck?
I fastened corrugated tin to the bottom of my deck on a mild grade, then put lattice on the sides and planted climbing nasturtiums. Lawn mower, tiller, spreader, aerator, clay pots, ...all sorts of odds and ends are under there now. Of course, there is no house behind mine, so no one can see it to complain, looks fine from the side. In the garage itself, bicycles are hung on the wall. I installed a high 16" shelf on one wall to help get stuff out of the way.
For airplane parts, I strapped the stabilizers and rudder to the ceiling in the garage, above the garage door while open, and put the elevators and fiberglass components in the attic to get them out of the way. My work table is large 8.25' x 4' and I put a shelf underneath to store parts waiting to be assembled. On the floor under it is all my "scrap" lumber that manages to be used all the time for something.
You should be able to get her car in there during the empennage phase, but once you fabricate or setup a wing jig, her car is going to become very acustomed to the elements. Hope she has heated seats.
When you get the empennage kit, be sure to cut out one of the faces of the packaging cardboard with those famous words on them and mount it prominently in your garage. (Oddly enough I didn't, and kick myself every day!) Don't worry, you'll know exactly what I mean when you get it.
Also, get honest with yourself and sell stuff you won't be using much, or give / throw it away. There further along you get, the more room you need.
Good luck!
