Framing and Sub-Flooring - 24 foot span with spliced 2x12's

I am building a shed type cover, measuring out at 28' x 24'.
I am only building half of it which will be 16'x24' to the center. I will add two more posts later having another 24' span 12' away.
cover sketch (http://s233.photobucket.com/albums/ee137/HARDWORKNWORRY/?action=view&current=cover.jpg)

I need to span the two 24 foot sections, and I only have 2x12x16' lumber. Can I splice a double 2x12 with offset splices and make that 24 foot span and add bracing about 3 foot on each side? The center section will be 10'-8" high and the low sides will be 9'-8" high.

I plan on 2x8's on 24" centers for the 16' long and 12' long roofing joists. Adding 7/16" solar board over those, alternating pattern and then laying R panel sheet metal on that.

Thanks in advance,
Turbopiper

A little hard to understand the question but the short answer, I think, is no. Why not buy the proper size lumber to do it right?

Bill

A little hard to understand the question but the short answer, I think, is no. Why not buy the proper size lumber to do it right?

Bill

I need to span 24 feet across two post as this pic shows (http://i233.photobucket.com/albums/ee137/HARDWORKNWORRY/cover-2.jpg), that will have a minimum live and dead load. I will add braces 3 feet from the top.

I was wondering if making the beam out of two or three spliced 2x12's would work, and bolting or screwing them together like this (http://i233.photobucket.com/albums/ee137/HARDWORKNWORRY/cover2.jpg)

I want to do this with 16 foot long 2x12's, as that is what I have on hand, and about 20 of them.
The local Home depot doesn't sell 24 foot long 2x12's, the longest they have is 20 foot.

Does that explain it a bit better?
Thanks,