IME better q cells are produced in a full-sized colony, complete with a
good force of foragers, lots of brood, a large provision of pollen, etc.  I
also feed them w/sugar syrup while the cells are being built, so there is
no lull in the food supply coming into the colony during this time.  They
have access to syrup 24 hrs., no matter what the weather.  The queen and a
couple of combs (brood and bees) are transferred to a nuc-box temporarily,
and by the time 10 days have gone by there are a good number of fine capped
q cells in the main colony.  It can be then be divided up into nuclei, or
the cells removed for use elsewhere.  Not too fancy, but it seems to work
quite well.  Without a strong colony, you can end up with lots of runty q
cells, so the more bees you can shake into a cell-building nuc (such as
John mentioned) the better.