Rhino, I used 2 X 6 X 3/16 on my 5' X 10'. I however cut lots of 1" plate. I feel that the 3/16" wall is very little more than just what is necessary for my table. Keep in mind I have no center supports to make cleaning from underneath the table much easier.
If you are going to have legs along the rails like most people build these tables the 3/16" should be more than necessary.
If you haven't seen one of the home built tables in action it would be well worth your time to visit me or someone else tosee one in action. You'll get many ideas to help you along with your build.
If you want to come by you are welcome. Send me a private message & I'll give you some contact information so we can arrange a convienient time.