Don't bother to buy drone foundation.  Just put in starter strips of worker
foundation.  They bees will then produce as many drone cells as they require
depending on many variables; genetics, season, strength, flow, weather, etc.
I bought Vince Cook's book (he even autographed it for me).  The first year I
used the system it worked perfectly but I have had very little success since.
Perhaps I add too many of my own ideas and don't stick closely enough to the
mastr's words.
Chris Slade