Hi ya'll and Bob,
 
If you wait until you KNOW those bees need another hive body or super you
are too late.
 
With a new colony on foundation I feed heavy to help insure my
investment.  Starting with a division board feeder until all but two
frames are drawn then replacing the internal feeder with more foundation
I switch to an entrance feeder until ready to add another box.  Here
along the Gulf Coast I use a single deep hive body for brood rearing so
the first addition above the deep brood box is a honey super.  Hives here
with double brood boxes don't produce a large surplus crop for me.
 
If you are setting up for two story hives I would suggest adding the
additional box now and continue to feed until the second story is well on
the way to being drawn and filled with stores and brood.  As long as
there is a strong nectar flow or supplemental feeding the bees will
probably not chew up the foundation to use the wax else where for comb
construction.
 
Don't cut your bees short on the feed.  A $2 five pound bag of sugar
mixed with a half gallon or a little less of water will yield about a
gallon of feed syrup which is cheap compared to the stress on that $40
package when they have to bring in all the required raw materials.
Estimates vary, but about 6-7 pounds of honey are required to yield a
pound of wax.
 
Best of Luck,
 
Rick Leber, Beekeeping since 1987
Mobile, Alabama