The rule for building a reloading bench is: The heavier, the better!
You need weight to hold that press down when you full-length resize cases.
The easiest and cheapest thing to do is find a good used STEEL desk. Dimensions will be about right to keep everything in easy reach. Bolt a 1 1/2" thick SOLID door to the top. Drawers and storage are built in.
If you are determined to build your own, make it like this:
I'd start with 4"x4" posts for legs, braced up with 1"x6" horizontal pieces, storage shelf 12" off the floor, and multiple shelves or small cabinets on top. Room for reloading manuals, die sets, small tools and accessories. Top should be a minimum of 2'x6". Bigger is better.
The top should be 3/4" thick plywood minimum. Two thicknesses are even better, then you won't have to reinforce the front edge with a 2"x4". That front edge takes a lot of stress when case forming or resizing.
Some people swear by a top made from edge laminated 2x4" nailed and glued up. That is REALLY heavy-duty!
Height should be comfortable for you when sitting on a tall stool or standing up. About 32-34" is right.
Plan for lots of storage space for cartridge cases, tumbler, bullets, die sets, case trimmer, powder measure, etc.
HTH
John