Alan in Little Washington (NC)
I'll be contrary here. IF you have the headroom- forget a horizontal rack and go vertical with wood stacked "soldier style" edges towards the wall. Benefits:

• Requires almost no structure
• Easy and quick to build
• The floor supports the weight
• Easier AND SAFER to load and unload (no step ladder or stool required to reach high boards). Safety chains recommended however.
• Can easily examine both sides of all boards
• Any board can be selected- no re-stacking needed to get "the" board at the bottom of a stack
• Doesn't take any more space, actually less, than a horizontal rack
• No warping if wood is 20% MC or less. A few "average" woodworkers do it that way- Sam Maloof, David Marks, Lon Schleining, many Woodcraft stores, etc.

I and many others store vertically: