Minimum skill for this project and reasonable skill with power tools. I saw this at my local hardware store and thought I'd give it a go. I do believe I will waterproof it since it will remain outside.

Step 1: Materials and Tools -

Materials:

2 1/2 inch deck screws (two dozen or so)
2 Five Step Stair Stringers
3 2x4's (16 3/4 long)
2 2x4's (46 3/4 long)
1 2x6 (13 5/8 long)
5 24 inch Window box planters
5 2x6's (20 inches long) Optional

Tools:

Circular saw
Power Drill/Screwdriver
Speed square (for straight cuts) optional

If you have to purchase the materials you can expect this to run you 40$ or so.

Step 2: Assemble the Stringers

Attach two of the 2x4x16 3/4 to the back side of the stringers -
The top edge needs to be square with the top edge of the stringer, and the side of the stringer. Ref 1 will identify what I am trying to highlight. The lower cross support just has to be square from side to side. Square up the bottom ends before tacking the cross piece. I used only one screw on each end to fix it into place.

Step 3: Attach Uprights and Cross Piece

I used a spare 45 inch to prop up the stringers. (Photo 1). It made it much easier to affix the (46 3/4 x 2 x 4) uprights. Install one butted in against the top cross piece, aligned with the edge of the stringer (see photo 2, ref 2). In the same manner I used only one screw to tack in place. Repeat process for the other other upright.

Once the uprights are in place, attach the lower upright cross piece on the inside edge. Align squarely with the bottom edge, and sides of the uprights. (See photo 2, ref 3)

Once assembly is at this point, ensure that everything is as square as you can it, then add the other screws at each connection point to secure the structure.

Step 4: Reinforce Upper Edge

Using the reinforcement piece (13 5/8 x 2 x 6), secure it with the screws from both sides. (See photo, ref 4)

Step 5: Final Notes

While it is a streamlined structure, it is not light by any means. So that it can do double duty, I cut some additional 20 inch 2 x 6's (see ref 5). It's heavy enough as it is, no need to add the additional weight.

While I did use weather treated materials, I do plan on using some stain tinted weather seal to make it more appealing.

Hope you like it as much as me. Quick, Easy, Fun