i have used scaffold boards to.
i spoke to a friend who runs a scaffold company and asked him for some of his condemned boards. after sorting through a huge pile of scrap boards and picking out the best i ended up with 11 long boards (10'-13') and 11 short boards (5'-7').
i also got a pack of 2"x2"x5' timber stakes and used these at the corners, i used such long ones due the fact i can knock them right in until they wont go in any further and will still have plenty above ground to attach my boards to. any excess can either be cut off or used to attach netting to.
i paired all my boards up to make a kit of parts resulting in 5 beds, fruit, potatoes, alliums, brassicas and legumes. average bed size is about 12'x6' which is a bit wide but i use the spare short board to stand on if i need to reach the middle which stops the soil getting to compacted.
i made all my paths 30" wide as it allows me plenty of room to get my wheelbarrow down. the only problem i found was due to the fact my plot is on a quite severe slope. this is great for drainage but not so good for level raised beds. 2 of my beds had to be made 18" high on the down slope side and at ground level on the up slope side.
im still in the process of construction on my plot due to only taking it on in February, still got a shed and greenhouse to complete along with four more raised beds, a patio, a mushroom tray, a more substantial netting system and a leaf mould cage..
oh and while im doing all that i still need to do ann the usual stuff that comes with running an allotment plot, weeding, sowing, harvesting, digging oh and not forgetting the eating!!!!