Joel uses several pieces of timber – it's better to be safe than sorry, so aim for roughly 20m of wood and cut them into three pieces. Six metres worth of 90mm by 35mm timber will set you back about $18 at Bunnings.
Joel's design is simple – he's effectively glued together three pieces of wood cut at varying heights to create holders for the bar. Where the wood is cut at the top, he's used a reciprocating saw to create a sloped groove that basically looks like a hook. The olympic bar rests between the groove and the piece of wood attached behind.
You can see the visual below:
To support the legs of the rack, you'll need a couple of buckets and some quick cement – the difficult part is getting the legs dead in the middle to make sure the rack is even and the posts don't fall under the stress.
You can watch the full process below: