Do you have a cut list or plans for the rear slide out? Looks good!
If you look up top you where the legal pad is you will see my chicken scratch of the boards that I used, but I will make the list a little cleaner for you.
Most of these boards were purchased over at the pine section at your big box store.
-(2) 1x6x8ft used for the sides, drawer face, middle board, and back of the case.
-(2) 1x4x8ft used for the drawers.
-(2) 24x48 pine panels used for drawer bottoms
-(1) 48x48 to be used for the bottom. It was super thin, I can not remember the thickness. I used this so the 1x6 wouldn't rest on my carpet, and so that it slid in and out easly.
-(1) 48x48 to be used for the top, again I do not remember the size
-(4) furniture flush nuts. Used on the inside to tire eyelets bolts to.
-(4) eye let bolts
-(2) 2 pair 150lbs 28 inch drawer slide sourced from Amazon.
-(2) 2 latches sourced from Amazon see above.
I used truck bed spray on liner, and I actually don't like it.
It holds dirt easily, and if I were to do it over I would just paint it.
The 1x8 were cut at 32 inchs times (3) plus 41 inchs for the rear.
Once box was secured to the bottom I measured drawer faces.
The 1x6 were measured while inside of the box, maybe 28 or 29 inchs I don't really remember.
Good luck.