My home welding table is 5/16 plate and I guess 36 x 60 " . It ( top ) was at an Amish place that was going out of business.
The table itself is 3 " square tubing legs with a band around the top and a band about 6 " from the floor. The floor band has some pieces welded to it for stowage ( I have a short barrel under there for plasma plummies ). The table is 36" tall and is perfect working height for me to weld on ( and plasma cut off the edge ). YMMV and you will need to experiment. My anvil height is 33 1/2 " . Tables need ground from time to time ( to clean them up). Scott (Dodge) brought up some good points about mass in that table will get slapped from time to time. I have worked on 1" plate tables and I have worked in booths that were 1" plate on the floor ( and grounded to 2 welders ). Build what you want from ground up. The back of my welding table is connected to my forge which is connected to my swage stand ( which has the leg vise ) and the gun reaches the vise. I can also reach a bit further so I can just use some rod or whatever to complete the ground loop and weld out in the middle of the floor. You will from time to time tack a fixture to a table or just build a fixture on the table and weld up from the flat table. Short answer is your welding table should be big enough to build what you need and also for larger projects when you may have them. This said, you need to be able to walk past it in the shop and that is hard to do sometimes in my shop ( things are crowded a bit ). I also have an acetelyne welding station on the backside of my table.