If you are putting a big and thick enough piece of plate steel on top of a table saw to make it into a 'welding table', I -sure- don't want to get you mad!!
Woodworking is woodworking, and welding is welding.
To me, the idea of a welding table is to :
- not catch on fire while welding or grinding. So, don't make it out of wood or plastic.

Steel works nicely though.
- be big and sturdy enough for welding, clamping, or BFH 'persuading' of a workpiece as needed.
Sparks, molten metal, grinding dust, oil, oil-removers such as acetone/etc, and what not really don't seem like a good thing to put or have around a table saw. YMMV.
TIG on 'small' parts? Maybe do a 'Jack' and put a fold up/down table along a wall and do the welding there. Done welding and then fold up/down the welding table/plate.