What can i use for welding table?

A welding table needs to be a reasonably thick steel plate, as it often is used as a base to set components up for welding using clamps, etc.

You might find a suitable piece at a scrap dealer or offcut steel dealer or engineering business using steel plate, and should be of a suitable thickness to withstand hammering etc. It needs to be sturdy, so an underframe of e.g. steel angle iron should be welded under it but clear of the edges several inches. Angle iron legs can be welded to that frame.

Preferably its surface will be as it comes from the mill, scale and all to prevent spatter sticking to it. However that will mean earthing your welder to the work you are doing, but you should also earth the table to it as well, and preferably run an earth wire to a good ground connection outside your workshop as well.

The danger using wood is it can possibly be ignited in such a manner it might just smoulder, and then later catch fire. Note you should also cover any timber in the vicinity of the table with sheet metal in order to prevent starting a smoulder in it.

If you are also using a disk grinder on your weld jobs, remember it can start fires as well.

Only weld if you can vent the area suitably to prevent breathing in the smoke from welding, and use a mask for welding and grinding (and safety goggles as well when grinding) to aid keeping dust and fumes out of your lungs.