It's been suggested that a (small) ping-pong table would be a good idea
for the kids; due to space constraints the proposal is to make a
table-top version which will sit on top of our (very sturdy) 6'x3'
dining table; the add-on will actually be 1880 x 1046 mm, ie slightly
overlap the underlying dining table in the same proportions as a
regulation table-tennis table.

The idea is to make this in two halves (ie cut along the net) which can
be removed easily to recreate a dining room at will; I was going to
attach lipping underneath around the edge to bear against the edge of
the dining table, to hold it in place. Top will be in 12mm thick board
I think (compromise between weight/durability/ball bounceability).

So, the question: what sort of board would I be best using? In real
money, we're talking two sheets approx 4'x3'. I'm thinking ply or MDF:
which would be best in terms of resistance to warping, given that it
will be used in a CH house and probably stored vertically in a garage
when not in use?

Thanks
David