You might try searching the cage and habitat design formum, I seem to remember someone recently asking about racks for pits. There are a lot of experienced builders on that forum and they can be very helpful (see Chris Harper).
I seem to remember them suggesting using hollow interior doors for the shelves of the large pit racks. They said you can get them cheap and sometimes for free if they have slight damage.
One other point they made is to be careful in ordering your tubs large enough. They made the point that the dimensions they advertise are the top of the tub and they taper down slightly so that they stack inside each other. So the dimensions that the snake will be using are actually smaller than you intended to provide for your snake.
Pits are large, active snakes and deserve plenty of space.
Good luck,
Kirk

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1.1 Jungle Carpet Python (both gorgeous)
1.1 Ball Python (normals, he said proudly)
3.3 hatchling ball pythons (normals)
1.1 Ball Python (het for albino)(gonna make my own albino)
1.1 Corn Snake (Okeetee, Sunglow x Snow)
0.1 Gray band Kingsnake (Blairs)
1.1 Desert Kingsnake
1.1 Pueblan Milksnake (normal)(Apricot)
1.1 Andean Milksnake (Inca phase) (het)
0.0.1 Bullsnake (normal)(my garbage disposal snake)
1.1 Bullsnake (red bull) and (het red bull)
0.1 Black Pine Snake need '05 mate!
1.1 Southern Snow Pine (snow)(red phase snow)
1.2 Checkered garter snakes (albino pair & het female)
1.0 Rhodesian Ridgeback (Hondo)
0.1 Spouse (WC)(hates the herps,and not real crazy about the dog)