I use the aluminum RCBS universal base plates on my bench and also on a nearby desk to hold any RCBS product that needs to be bolted down. I secure the base plates with bolts for permanent installation or large "C" clamps for removable option.
Design your bench heavy, then double that. Reloading benches need to be very well built and secured to the wall or floor to prevent movement.
I found a company in Montreal that makes custom workbenches for labs, commercial businesses etc. The benches have extensive pullout drawers built in, can hold up to 200 pounds each, fully adjustable for spacing etc. Cost a few $ but I only hope to buy it once. It is superb - two inch thick butcher block top, five steel drawers, holds three presses and a measure or more, extra full width top shelf for stuff. Just wish it was bigger but no more room. Excellent suggestion re metal storage cabinets, I went to a commercial office furniture distributor, got several pieces of scratch and dent cabinets that are like new.
Another good suggestion is to install a 5" bench vice where you will be cleaning and working on guns. Vice is essential, get one and you will find out how handy they are. Also get some padded (felt, leather, rubber) pads for the jaws. Only way to clean a rifle is to clamp the barrel in the vice, work on rifle from the receiver end. Until you get one you will not realize how important a vice is. Also lots of light as suggested. I use track lighting, works nice and an oversize florescent light over the work bench.
Good luck with your reloading bench and gun room.