This method will make a frame about four and a half feet high, just under four feet long and a foot and a half wide. I'd use a frame of this size to grow three cordon-type tomato plants. Or a row of peas, if you add a few spiky twigs for them to climb up.
You will need:
Set of three 5ft bamboo hoops (available from garden centres)
Five 4ft bamboo canes (you can use more if you want extra bars on your frame)
Put five rubber bands on each hoop, one at the top and two on either leg, at a roughly equal height (you can adjust them later). They should be tight enough to grip the poles but still manoeuvreable.
After preparing the soil, lay two of the bamboo canes out on the ground as measuring rods, then position the hoops along their length with equal spacing. The outer hoops should be an inch or so inside the straight poles.
Hook a pole through the lower rubber band on the central hoop, and then hook either end of it into the bands on the outer hoops. Do this for all five poles. You will then have a nice sturdy structure. Try to make sure the poles sit on top of the rubber band, so that it acts as a support underneath.
Tie some string tightly around each rubber band joint to give the poles extra support. Why do you need to do this when the rubber bands are already holding it pretty securely? Well, try leaving the rubber bands out in the sunshine for a few weeks and you'll see what happens.
And here's the finished article, complete with three Black Plum tomato seedlings. Yes I know they look sweet and innocent at the moment (in fact they're so miniscule you can hardly see them) but they'll soon be splurging over the top of the frame.