How to build our containers?

There is a garden centre down the street from us selling lovely pre-made wooden containers, two metres long and one metre deep, and about 50cm high. They come apart for storage and easily slot together once the garden is ready for them. They cost $129 each, but for the convenience and neat appearance I think we should get a couple. My husband thinks we can make our own but I think they'll just end up looking slightly crap (like the "compost heap" I can see through the window right now, which is a pile of dead leaves surrounded by decrepit pallets and rotting sections of picket fence). I'd much rather pay for something that looks like a professional put it together!

Having said that, Mel's book says that for all but the long root vegetables a six inch depth of soil is all that's required, so those pre-made containers are deeper than we need for most of the garden. Mitre10 sell fence palings for $5 each which could easily be nailed together to make a low container, but they're also treated and I don't know what they've been treated with. It wouldn't be good to have chemicals leaching into the soil, then into the vegetables, then into our mouths. I've emailed Mitre10 to ask them how the wood is treated, so we'll wait and see what (if anything) they come back with.