Start looking on trademe for some speed shelving, of various lengths. That will use wooden decking, which you can make from shutterply and timber if you have to ,or just use what it comes with or order new to size. Get some that will go almost all the way to the roof, and preferably with 3 rows per unit. Bottom feet have the lowest one placed just above them, then another at waist height and the top near the roof. Get a good ladder as well, and then you can have a work area and storage both under and above, and with the lower above the floor you have room for air to circulate to keep them from getting musty. As well provides some flood protection. Plus you can sweep the floor under it, or use the vacuum to clean there. The shelves will withstand 1 ton per bay for each level, or you can walk on it if needed.
I have one at work storing PVC sheet, and it has 4 tons of film roll on it, in a 2m length. For that one I ordered new and ordered the high strength beams, 5 sets, at about double the price. The uprights though are standard. the fun was putting the 30kg rolls on each shelf when stacking, that was hard work, took 2 weeks to do the trips to the slitter to collect them in the van and load and unload at each end.