Here is the HDPE i picked p for free.
It measures 5' x 4.5' x 1"
I have 3 that measure that size, as you can see in the picture, and another that is 4.5' x 3' x 1" which is also in the picture.
I'm planning on builsing Joes second machine, in preperation for building his 3rd one (at some undisclosed future date)
as you can see, its blue as all get out.