DIY Tent Materials?

I've gone through a couple different tents for backpacking
I continue to be unsatisfied with
-Space
-Weight
-set up
I decided I was going to make my own tent and what I'm shooting for is a light weight, roomy tent that can be set up with two trekking poles, because I like my trekking poles.
Heres where I'm stuck. What light weight materials is a tent made up of, mostly I'm concerned with fly material, I figure I will mostly use some sort of screen for the main tent, so I have a very airy open space for summer nights. But a goal to create a fly that can stand 3 seasons.
Any leads on fabric/ treating said fabric for water proofing.
or were to buy fabric. Thank you all.

Unless you are prepared to use some of the more exotic materials such as Cuben, it's hard to go wrong with 1.3 oz/yd silnylon for the fly and 1.1 oz/yd ripstop and no-see-um mesh for the tent body. You can get all of this from Quest Outfitters or Seattle Fabrics; Google them, they both have online catalogs. They also stock the clips and buckles and cord-locks you will likely need.

Now, in my experience, it is difficult at best, to duplicate or better what tent making firms have to offer your first time out. You will need to learn by doing and mistakes can be expensive. You will lack the experience and knowledge tent makers have acquired over the years and usually at considerable expense. Please don't think I'm saying you can't make a great tent though. I am saying that you probably won't save any money.

I agree with Pika...

also, in case you didn't know Henry has instructions online how to make his original tarptent. It sounds similar to what you are looking for, it might be a good place to start:

http://www.tarptent.com/projects/tarpdesign.html

Thank you for the info on material. I will check out those websites.
As far as trial and error, I may play around with some sheets from good will to get a basic platform. I plan on having a pretty simple design that will be like a lean to with two trekking poles holding it up and lines to stabilize the shelter. I have been poking around the internet at some DIY designs as well.

I like the design of the MRS fast stash

I suppose as well I did not realize the price of these materials. May just purchase a MSR fast stash

If you like that design you could also search under Whelen tents # ,Walrus (or MSR) Trekker Tarp or the MSR Missing Link.
The Missing Link came out when MSR had problems with the PU coating on their flies so be careful if you buy a used one (sticky fly)

#http://www.backpacking.net/makegear/huntersleanto/