Step 5: Nail roofing material to panels
Drive galvanized roofing nails liberally to secure the roofing material to the frames.
A finished 2x4 frame should look like the one in the first photo. I don't think it matters which side you face out. I chose to face the black side out, however ondura comes in a variety of colors and you might wish to face the color side out.
I had roofing nails left over from another project and used both the standard nails and the ones with the plastic caps. I found the plastic cap nails to conform nicely to the curves of the ondura. Overall I liked using those better than the standard ones.
The second photo illustrates a completed bed.. you can see the roofing nails in it. I tried to space them fairly evenly.