Stacking computers

I have a serious questions to ask. How high can you pile computers and not damage the bottom units. I have computers stacked along my garage walls. For example: MicroVAX II on bottom, three 3B2's next, AT&T Unix PC next, box of keyboards above, empty boxes and boxes of cables on top. I wonder if pile stability is the most important, or that the heaviest stuff be on the bottom, or is regular shape items on the bottom best. Seeing the floor is not a problem. I'm trying to buy some shelving from a friend in St. Louis who gets it cheap. Although cheap shelving is an oxymoron. I envision some stainless steel roll around shelving and some fixed units. Of course if the New Madrid Fault reactivates I'll just have to restack. Can anyone guess what the average per foot floor load is for 3' high computer piles? I'm afraid that my garage attic may collapse on the cars if I stack it higher than 3'. I'm also worried about the temperature extremes in the garage attic. I'm lucky my wife and I have several small power and sailboats and guess what boats live outdoors with no complaints about rain, snow, heat and cold. When my kids go off to college I'm converting 1 or more bedrooms into workshops. Thanks Mike mmcfaddden(a)cmh.edu