Have used one many times and it comes in handy. I used to have a 2x4 but it ended up being too small and sold it. If I can ever get my shop done, I plan on building a 4x8, I would go with 1/2" plate for the top. Maybe overkill but I would have concerns about warping with 3/8.

I have a 4ft x 5.5ft 3/4 in plate.

I just got rid of this 4x8 and cut out two 2.5x5’s that we can bolt together when needed. The 4x8 tables we end up with 4x2 of workspace and the rest is just cluttered up. For the f clamps, I use the harbor freight cheap ones and weld a 5/8” bolt to the bottom.

As far as usability, I like to use it every now and then to hold stuff square but not as often as I thought I would. If you were to be doing some repeat parts, the holes are cool to use to bolt stuff to. We have some attachments we use like a pipe bender that can be bolted to the sides wherever we need it.

They’re 1/4”, that 4x8 was also 1/4”. With the grid underneath it was just as stout as our 1/2” plate table, but easier to move

I’ve got a 4X4 and a 5X10 I used all the time back when I had free time but I think anyone who likes building things needs one in their shop. I highly recommend building them with jacks and steel rollers integrated into each end so they can be lifted and rolled around easily. I put wheels on my little one when I got it and it moved around to much but they’re to heavy to move without them. I can raise all of my welding tables up and move them anywhere in the shop within a couple minutes by myself and one weighs well over 2000 pounds. You can also build them shorter and raise the deck height up by adding spacers under the legs with the jacks.

I’d say 3/8” at the minimum but I’d personally go with a 1/2” simply for the added weight and helping stabilize it from warping, both of mine are 1/2” and it makes a difference. I had a small one out of 1/4” and a larger one out of 3/8”s and when I upgraded I was glad I did.