Graphically illustrated instructions for building and installing T-Frames are contained in the Mittleider Gardening Course – advanced section, Chapter 15, as well as other books. Here are the “guts” of it. For a 30′ Soil-Bed or Grow-Box, buy 6 – 8′ treated 4 X 4’s. Cut two of them into 6 equal-sized pieces 32″ long. Four 32″ lengths become the top of the T.
The other two 32″ 4 X 4 lengths then are cut into 4 equal-sized braces using 45 degree-angle cuts as follows: Measure and mark 10 5/8″ along the bottom edge, then 3 5/8″, then 10 5/8″, then 3 5/8″. On the top edge, measure and mark 3 1/2″, then 3 5/8″, then 10 5/8″, then 3 5/8″. Draw lines between these marks, then, using a table saw, cut on the lines.
Pre-drill through the top center of the 32″ tops, then use a 6″ spike to nail into the 8′ post. Screw or nail the braces to the top and post. Bury 15″ in the ground at 10′ (or shorter) intervals.
Use #8 gauge wire and eyebolts between the T-Frames, or use 1/2″ galvanized pipe (held in place by two nails). If you want to extend the growing season, use 2 X 4’s on edge, and make an arched canopy with 3/4″ PVC and 45 degree Slip fittings every 2′, then cover in early Spring and late Fall with 6 mil clear plastic.