For some strange reason they are building 2 story houses where the roof of the garage is just a bunch of open space.
If you want more storage space than you can probably use build wood shelves that hang down from the ceiling. We've done a couple of them and you can't imagine the amount of storage you can make out of all that wasted space? We have even built ladders on the sides of them so that you can get to the shelves you want just using a safety ladder.
Getting up to that high ceiling can be a bit rough. I have a 14 foot safety ladder that I can borrow.
We build the base out of the shelves out of 2x4's with one center cross support. We make the base an even 4' by 8' so you can just lay your plywood in and tack it with a few screws.
Scuba tanks are one thing are hard to find a place to store. On the bottom of the bottom shelves I took some nylon strapping and just put four on either side of the center support. My tanks just slide into the loops and hang from the ceiling. For some strange reason everyone refers to them as my “Bomb Racks.”
I thought of it when I had a one story garage that just had a main center beam. I put 4 off of the center beam and 2 over the garage door. Just six 4' by 8' shelves made for a lot of storage.
If if you have joist of even a drywalled garage ceiling you can make a lot of extra storage.
You'll never have to crawl into you attic again.
One little trick that my dad thought of. Do you always tend to pull your cars too far into the garage?
Mark the right spot you want to stop and hang a tennis ball from the ceiling by a string. Stop your car when the tennis ball touches the windshield and you always have the most room open in the area in front of the cars where every thing in most garages is.