What kind of tubing would I use to make custom road bike frames?

Also I want to get a welder soon and I was wondering what kind I would need to use on steel and maybe cr-mo? Thanks in advance!
PS where could I get the tubing?

I could go on about this all day...

Might I make a suggestion?

I think it is a good idea to do a bit of research on what you are trying to do. Being a master framebuilder I see many people that decide to "get a welder" and build a bike frame. It ain't that easy. Read some books or enroll in a night class at a technical school.

Other than the fact that you need to do some pretty accurate pre-machining you'll need to decide which kind of welder you are using- usually MiG or TiG. Electric arc welders are not generally used. TiG (Tungsten Inert Gas) is the most common in framebuilding but takes great skill. If you are brazing, then you need torch skills- again, not something you learn overnight.

Steel and cr-mo are the same material (this is why I suggested you do some research first) but are variants of each other. Hi Tensile steel, or 1020, is commonly used for bike frames as is Chrome Molybdneum (CrMo), or 4130. 4130 is about 4 times the cost of 1020 and is much stronger for the same size and thickness tube. By the way, CrMo and Hi Ten are both the same weight... the reason some CrMo frames are lighter is because the material is stronger and so less material is used... less material=less weight.

A worthy note... the world supply of molybdneum has been all but wiped out so as time goes on you will see new steel alloys to replace it.

To the answerer who suggested you use Ti... DON'T! Ti needs to be welded in a nearly sterile environment and exposing a hot weld to oxygen will destroy the structure. Again, look before you leap.

Titanium would be your best choice. It's ligher and stronger than chrome-moly steel. Get a welder that is an expert at TIG/MIG Welding. Where to buy? I don't know where you live so I don't know the metal supply companies in your area, but your welder will know!!

Ask someone who does it for a living - for example:
http://www.grognardbikeco.com/

I bet if you sent him a message, he'd be happy to help you out. As I understand it, there are specialized classes given for prospective framebuilders. It's not as simple as you'd think.

Materials:
Aluminum
CroMoly
Steel
Bamboo (yup)
Carbon Fiber

nearly all custom frames are custom because they are made out of materials other than normal (aluminum, cro mo, etc.) and they are designed to fit a specific person. most custom stuff i've seen is usually titanium or carbon or both. making carbon frames in your garage doesn't sound too easy....

If you're making your own, you should start out using plain old hi-ten steel, which is designated as 1010. The reason being, it's easy to work with for beginner welders, and it's cheaper than chromo or aluminum alloys. Make all your learner's mistakes with 1010! If you get into it, your first one won't be your last one, and you can always move up to thin-wall chromoly (4130) and other materials as you get more experience with welding.

As far as what kind of welding to do - it's your choice. The easiest to learn and still produce good results is good old-fashioned brazing. I've heard of people getting good results with wire-feed MIG welders, but with the thinner walled tubing it can be tricky to avoid blowing holes in the frame when you strike the arc. Aluminum is much trickier to weld, because it's such a good heat conductor that when you make a puddle, you're extremely close to melting the entire frame.

For more specific answers, you should probably find a builder's forum on the Internet and ask questions there.