A few years back I copied another members idea using 3/4 Oak plywood. It sits on top of the rails for a carpeted bed and still clears bottom of the tailgate when closed.
I posted it somewhere, but this one link recently was posted so I added it here again
1. I first made a pattern out of poster board
2. transferred to 1x6 so it could be removed easier while working on project.
3. I then transferred to chip board for pattern using flush trim router.
4. Removed bed cover and test fit chop board.
5. Used chip board and flush trim router to create oak bed floor.
6. Routered some channels for polished stainless run strips and polished stainless 1.5 inch corner guard for end cap.
7. Stained board
8. Cut strips and end cap to proper length and glued to finished board.
9. Stapled welting around perimeter of board (the inside of truck tapers - the welting fills the gap that would would see without it, the pattern is not perfect and truck carpeting is not the exact same on every truck.
10. Designed a pocket edge for hinges using a CAD, program. I had them 3D printed to finish off the look.
You have many options after you create the main piece. Paint the edges, use iron strips for edges, surface mount thin stainless or painted strips, painted wood or router in different wood and then stain!.
Once the cargo cover is removed and this floor drops in easily in one piece with assistance at an angle - dropping it in and down towards tailgate and then lowering the front edge.
EDIT, I added last picture late. It belongs as picture #3, test fitting the chip board before using it as a pattern to cut oak plywood.
I also laid out the strips, I purchased 6 but liked the look of 5 better. That way one in center and two on each side, additionally more wood exposed, less distraction from wood. This picture shows 6 laying on top so you can compare to 5 in the other picture.