As others have said, it's super easy. I made two - one with just two 2x4s that fits 5 boards and cost less than $10 to make; and a nicer one for a friend with a 2x6 and 1-1/4" round stock (8ft full round moulding ~$10 at Home Depot) wrapped in black foam pipe insulation that cost about $40-50 (more if you need to buy hardware, tools, stain, etc).

Here are a few thoughts (sorry if this is basic info for you):

1. If you want it to be sturdy, be sure to use wood glue and screws, not just screws.
2. If you're using dowels or wood rods, it's better to use a spade drill bit to sink the rod into the backing board so that the rods don't move side-to-side.
3. Make sure you get your board spacing right. I store my boards with fins on and put my spacing at 8" on-center, but I think I could have fit one more board if I had gone ~7 or maybe even 6.5".
4. I put my rack at about 52" high, and it seems right for boards between 5ft and 9ft.
5. Make sure you're attaching it to the studs in your wall. Mine's bolted with lag screws so that I don't come in one morning and find all my boards in a pile on the ground.
6. On the ends I put two lengths of nylon webbing with a quick release buckle to keep boards from accidentally slipping out. At least once this has saved a board from falling onto the floor.
7. FWIW, I also have a ~$50 Portamate Lumber Rack for storing boards horizontally that's pretty great for the money. I extended the supports with 1" square stock wrapped in pipe insulation.