I am finishing the basement in my sister's 1890's house. The mortared
rubble foundation, although in good shape, is too "bumpy" of a surface
for flooring, so I am building a subfloor. My plan is to place a
heavyweight cross laminated vapor barrier on top of the foundation, use
asphalt shingles for shimming, and fix pressure treated plywood directly
to the foundation with concrete screws.

Code requires the ceiling to be 7', so I must keep the total flooring
height under 1.5"-- needless to say I'm thinking thin. I will be
installing either laminate or cork flooring, if she'll ever make up her
mind.

Anything wrong with this plan? Need I treat the foundation with any kind
of sealer before beginning? When installing the concrete screws, can I
drill the hole directly through the subfloor and then install the screw,
or will the resulting hole in the subfloor be too big for adequate
support? Tips, tricks, or warnings?