My husband and I built raised beds of landscape timbers held in place with BIG nails, or stakes slid down the holes we drilled in the corner sections and down the length. The height was about 2 ft, and the boxes were 4x4 ft, 8x4 ft and 12x4 ft. We took used 2L soda bottles and cut the tops of and put those standing in the bottom of the boxes. We had very sandy soil that wouldn't hold water for 10 minutes and the bottles helped to catch and hold water down in the ground to 1 ft line. The plants could then decide how damp they wanted their roots: either in the bottles or between the bottles. We then filled the box with soil appropriate for the food we were growing in each box. The advantage of several boxes is that you can create different soils for different plants.
When my father died, I got some of his books. He had one on square foot gardening. Broccoli, cabbages, cauliflowers, peppers, potatoes all require a 1x1 ft square for each plant. Carrots, parsnips, leeks and onions were 16 plants (4x4 rows in a sq ft) or 9 (3x3) per square foot. Watermelons, cantaloupes, etc needed nearly a 24x24 inch space on their own. If you put in a heavy trellis down the length of your 4x4 ft box at the one ft line from an edge, you are growing up and can get 2 seeds per 24 inch square: one on each side of the trellis (1 seed in 1 ft x 2 ft, the trellis in the middle there, and 1 seed on the other side. Our watermelons were whoppers so in my 4 sq ft box I planted a seed in each corner of the box (back about 6 inches) and let them sprawl over the edge of the raised bed. Green beans, black beans, peas, snow peas, etc. were planted with a string trellis down the center of 1 ft x 4 ft part of a box with 2 seeds ( one on each side of the trellis) and a total of 8 seeds per each foot square ( 3 in. spacing). Leaf lettuce, turnip, beets, head lettuce can be planted as 9 in a sq ft. You can also do herbs like this as well. If you harvest the outer leaves during the season, you can get 4 plants per sq ft.
This worked wonders for us and limited the space required for the garden, easy height for weeding, and easy to replant as your veggies came to harvest. We also sent any visiting kids out to the garden to get veggies for stir fries, stews, etc. They were so invested in the harvesting that they ate them all.