I grew up as an Air Force Brat, moving every few years and not being permanently attached to a house. So when it came time to create a way to store gear in the garage, well this experience played a roll.
As you can see in this photo, the shelving unit is made up planks of wood, and bricks. All you do is stand up a few bricks on the floor, lay a board across the bricks, and repeat as you work your way up. The materials are pretty cheap. The bricks are around $1 a piece. The wood in this case came from dumpster diving, however even a few sheets of plywood cut to size would work.
I have found this unit to be extremely strong and flexible. By controlling how high you stack up the bricks, and where you place them, you can custom size it for your gear.
As you can see in this photo the unit is holding a lot of gear.
How do you store your gear?