The first thing needed is something perfectly flat. I use
pool table slate.
MDF is no good in my opinion unless it is braced very well. Slate
"bend" under enough of a load, so it to will need to be
have a carpenters straight edge around to constantly check for flatness.
Slate is available from any place that handles pool table supplies. This
particular piece I got out of the trash at a billiards supply store. It
a chip in it. Not a problem for our use.