To make a custom exhaust you will need the following: 

-Hack saw or metal cutting saw

- Clamps

-  Hand file or grinder of some sort

- Tape Measure

- Miter box if you have a hack saw

- Some metal tubing (round or square)

- an expansion tube (made from a large aerosol can, small paint can, coffee tin etc)

- Some sort of sound absorbent material (asbestos (causes cancer but is the best), cardboard, etc)

- Welder of some sort ( a person with a welder, an oxy/fuel torch or brazing kit, solder if you are using copper pipe or jb weld (this stuff isn't bad and its like a glue for metal, I wouldn't use it personally for durability reasons

I will tell you how I made my custom exhaust stack and than you can design your around my model or think up your own plan, totally up to you!

1st:

  Get all of you materials together.  Saw, clamps, Tape measure etc...

2nd:

Cut 1 piece of pipe approximately 7 inches long and the other piece about 2 inches long.  Cut 1 end of each of these 2 pieces at a 45* angle.  Weld them together.  Now you have a metal L.

3rd:

Weld the small piece of tube into or onto the exhaust manifold, spark arrestor or whatever type of exhaust system you have on your engine (where all the exhaust gasses come out, weld it on there!).

Now, you can stop here and have a loud straight pipe or you can have a straight pipe with a sausage muffler on it like these or you can keep going with the quiet pipe....like I did!

4th:

Get your self a small paint can or aerosol can.  I used a paint can.  Clean it out thoroughly with paint thinner, rubbing alcohol, engine cleaner, brake cleaner or soap.  Just make sure that all of the paint or whatever is or was in there is cleaned out and washed away with water. (this includes your cleaner choice also)

5th:

Drill holes into your pipe.  Only drill holes on the pipe where it will be inside of the can, not seen out side of the can.  (sorry about no real picture, but you get the point of it)

6th:

Drill holes in the bottom and top of your paint can to fit your pipe coming from your exhaust port.  Then drill small holes (a little bit smaller than a dime)  around the main hole at the top on the lid for exhaust gas's to exit the expansion chamber (paint can).

7th:

[sorry no pic 4 this 1]  Insert the cardboard piece into the the paint can.  Before putting it in, cut it to the height and inner circumference of the paint can.  Than, wrap it around something cylindrical like a pop can.  Than put it in the can and let it unfold itself to expand on to the walls inside the paint can.  Now the walls on the inside of the can are totally covered with 1 piece of cardboard.

8th:

Weld the lid on to the top of the can.  Once that is done, weld the pipe to the bottom of the can and to the top of the can where the lid and the base of the can is.  After that, weld a cap onto the end of the pipe that sticks out from the lid a little bit.  You now have what's in the picture above.  (the holes around the main hole where the pipe is, the cap on the pipe, and the lid welded on).

9th:

Paint the thing to make it look pretty, and FILE OFF ALL SHARP POINTS AND ROUGH EDGES!!

10th:

You are done done done!!!  Take some pictures and show it off to your friends!  Well ok, if don't than I will....

That's what mine looks like....hope yours turns out just as well!