This has been a work in progress, The concrete was the floor of an old warehouse, Large area with lots of old wood and rotted sawdust = raised beds, which cost time but little out of pocket expenses. We built each bed with existing wood, 5 ft wide is just a tad too wide, 4 ft is a tad to narrow, Any length is fine, we have used 4 to 16 ft lengths. Early beds were only 6 inch high but they dried out to fast, So they have been doubled in height. We did purchased some 4 " torque screws. Each bed uses 4 to 6 per corner. Too small of corner pieces allow ends of screws to protrude, but easily break off with pliers. We used to add corner wood pieces to the inside but found that they rotted just to fast, the exterior corner pieces seem to last considerable time. We filled each half full with straight sawdust, raked up maple leaves and mowed grass trimmings. then added screated topsoil with chicken, horse, and cow manure mixed with lots of rotted sawdust, mixed with a chipper shredder. As an added bonus worms moved in to feast on all the maple leaves, We grow Blackberries, raspberry's, potatoes beans garlic, lots of lettuce, chives onions, peas carrots Tomatoes of every kind, Peony's, many Amaryllis in pots that we must take in as they do not winter outside. And lots of miscellaneous flowers, We use no herbicides or pesticides, as bugs are little threat, and weeds well they just are.. Thanks for looking