The bench top itself doesn't necessarily have to be heavy, or unusually strong......But, strength is necessary where the press is mounted. My bench top is made from 1/2" plywood, but directly under the press, it is reinforced....very strong and rigid!
Weight, as mentioned, is a good idea. My bench is made from steel angle iron and square tubing. Besides that, there are shelves underneath that add to the weight.
I'm not suggesting that anyone should build their reloading bench just like mine.....but, if they did, it'd be suitable to the application. There are many ways to get the job done right!
The two main concerns are rigidity of the design, and stability. (Stability can be accomplished by either mounting the bench to the walls and/or floor......or, by weight.)
hogship