I already told you my story of how unfortunate was of finding one in an import shop and at a Nopi store near here. So since I am basically SOL. How do I do this with what material

 

I just finished making one for my 88 2 weks ago! You are in luck. It may sound pretty crappy but it actually doesnt look too bad and it works perfectly. First, you need to find a piece of metal. I cut out the bottom of an extra transmission pan that I had laying around. Then just mark out your 4 holes for the screws, and cut the center out to let the air pass through. I used air saws and other air tools to do this so I dont know how else you can cut it and make the edges look good. Here comes the funny part. Then I got a metal can from some gren beans and cut it to about 2 inches and welded it on to the other piece of metal. It happened to be the same diameter as the tubing I was using for the cai.After I welded it I epoxied all around the areas and made it all smoothe to look better, painted it dark grey and its ready to bolt on!!!

 

Unless you are interested in the experience of making one, it is easier to buy it.
Try this page http://www.ppsonline.net/underhood2.htm#adapt
for $16.95 USD (cheap ehh)
Good luck,