Before i get all these negative opinions and getting flammed, I am asking just for the knowledge. Not that i want to build it, i just want to see it it's possible.

I was wondering if you can fab your own upper intake? Say, using square stock tubing, or round tube. I know you pretty much can make it, as long as you have your vacuum lines and a TB bracket, but what if the length of the tube is longer or shorter than factory? would affect the way the truck runs/performs? Since TB and intake spacers are so popular, would it do much of anything? Would making your own is a specific design give you performance?
Also, would it matter if each intake lines have independent holes? or would 1 large hole intake do the same thing?

 

It certainly can be done but the design will affect the way the engine performs. The stock manifold has long intake runners for low end torque and low rpms. If it had short runners, it would produce high rpm horsepower. There are many things to consider when altering intake manifolds, it is a science that I happen to know a few things about but most of my experience comes from 4bangers. That being said, the science definitely transfers to V8 engines.
You should start by drawing out your idea on paper. Then fab something up and test it out. Good luck, let us know how it goes.

 

Yes you could build your own intake but it won't have the amount of effect you're thinking. Intake tuning is but one small part of an engine package, it can complement it and help to maximize HP and TQ potential but even if it's all wrong for the engine combo it won't drastically change the powerband, particularly when there are other components that drastically limit engine output(ie: the heads and cam).