I'm building a house 8 miles back in the forest - there are no
inspections.  I'm making 18" diameter concrete piers for the
foundation.  There are 25 piers spaced about 8' apart.  It's a 32' by
44' wood frame 1-1/2 story house. The lot slopes: there is a 12'
difference in height from front to back, so the front 5 piers are 12'
off the ground.  The entire lot is on a rock shelf so the piers are
sitting on the rock rather than dug into dirt.  I've drilled 3/4" by
12" holes (5 each pier) into the rock and pounded in 2' steel rods. 
There will be external steel bracing: 1-1/2" square tubing
horizontally and diagonally bolted into the piers with 1/2" bolts.  I
built another house just like this 8 years ago, but the piers were 5'
high and 4' into the ground.  Each of those piers only had 4 pieces of
3/8 rebar vertically - there was no wired cage.  The house still
stands with no cracks or any problems with the piers.  But this house
is larger and the piers are taller.  I'll have the cement pumped in,
but the kolumn forms are already in place and there is no easy way for
me to build a rebar cage and lift it into the form, or set the cage
then man handle a 12' cardboard form over it. I can't afford a crane
or an engineer and the other piers have had no problem.  So far, these
piers have 4 pieces of 1/2" rebar vertically - nothing else.  My
question: do I really need a large engineered steel cage inside the
piers?  Is there enough strength in the vertical rebar without
horizontal cross pieces?  I'm just looking for information, not a
legally binding opinion. I have photographs of the other house showing
the old piers under construction.