I have built 5 of these frames for my vegetable garden. The first two have held up so well, I decided to build two more and take the time to document the project. depending on the price of cedar, they cost about $55 each.

Step 1: Materials and Hardware Needed

6 - 1 x 4 x 8 Cedar boards
2 - 1 x 2 x 8 Cedar boards
4 - Simpson Strong-Tie Z-Max 7 in. 16-Gauge Steel L-Angle
32 - #8 x 1-1/4in Deckmate screws are used to attach the support pieces
32 - #6 x 3/4in for attaching the L-Angles

Step 2: Cutting Lumber to Size

You will need (6) 1X4x8 cedar boards. Four of them will be used at full length. Cut two of them in half. In this case, I am making two frames therefore there are four sets in the photo.

Step 3: Make Support Members

You will also need (16) 1 x 2 x 7in pieces cut from an eight foot piece for support members. Drill (2) 1/8in holes in each piece. On the centerline and in 1-1/2in from each end.

Step 4: Assemble Side Rails

Using 2 full length boards edge to edge and side by side with the rough side in, attach one Simpson Strong-Tie Z-Max 7 in. 16-Gauge Steel L-Angle to each end using the short side of the L-Angle. Attach using the #6 x 3/4in screws.
Next, turn assembly over so that the rough side is facing up, using two screws each, attach 5 of the 1 x 2 x 7 brace pieces: one on each end placed 1in from the end, one in the center and two at 24in from the center. Attach using the #8 x 1-1/4in Deckmate screws.
Repeat for the opposite side rail.

Step 5: Assemble End Rails

Using 2 48in boards edge to edge and side by side with the rough side facing up, using two screws each, attach 3 of the 1 x 2 x 7 brace pieces: one on each end placed 1in from the end and one in the center.
Repeat for the opposite end rail

Step 6: Final Assembly

You now have the assembly components needed for final assembly and placement onto your well prepared and flat ground.
Lay newspaper, cardboard or landscaping fabric over the 4ft x 8ft area letting any extra material overhang the area by 3 - 6in on all sides.
You can then, with the assistance of one other person, attach the end rail to the ends of one of the side rails creating a 3-sided box. Then attach the remaining side rail on top of the two end rails.
Place this frame on top of the base bedding material and fill with some quality soil and you are good to go!