12' X 28'...............now your into something more then most sign people are used to dealing with.
#1. take into consideration the sq ft of this 336...........
#2. lets just say when its completed you got 2 pounds per sq ft. 672 POUNDS. and it may be more depending on frame, sub-straight materials.
#3. are you INSTALLING IT???? now if you are, your going to need an engineer to sign off on it. because of it weight and if its up in the air..........your gona need crane or some kinda lift.
#4. better have insurance........during install and for after it is installed.
#5. so doing anything HERE....ON THE CHEAP.........
YOU may as well PASS......... on this job and let someone capable handle it.
CHEAP IS NOT GONA WORK HERE!!!!!!!!!!!!!!!!!!!!
NOW....... with all of that......like others have said.....a square tube frame......2 or 3 or 4 pieces, 4 would be best, that would give you @ 4 ft X 12 ft......so 3 sheets alumicore per panel 12 sheets total. 1 4 X 12 panel.....
ALUMICORE...... would be my choice for sign sub-straight for it less weight then MDO.
bolt the frame to the building, then install panels to frame......
my thinking money here would be in the $20 a sq ft range.........$6720.00-$8000.00
+crane/lift rental