i have just put a series of high level shelves at the back of my garage at home, im going to continue them all the way around. they are just high enough for me to not bang my head on them, but still gives enough room on the shelf for something as tall as aerosols.
i agree with Mini-Mad-Craig, get rid of stuff you arnt going to use! i have held on to stuff for years thinking i might need it, a few years back i sold loads off, and binned the rest, still havnt needed any of the bits since!
a friend of mine was renting a council garage a few years ago, he was lucky as it was one that has free electric inside. he then found that the two garages next to his were empty so started to rent them too. in a stroke of genius, he knocked them through and stacked the bricks up should he ever need to put it back! he had a triple width garage for next to nothing, with free electric!