Cage Building: Take a gander at my 1/6 Jeep build, only a couple pics, but you'll get the idea. Since it is a 1/6 scale Jeep, I used 1/4 inch brakeline for the rollcage. I bought a couple 6ft lengths of the coated brakeline, don't do that, get the uncoated if it's available. I had to sand/grind the coating off before I could brazed the pieces together. When you purchase the brakeline, it would be wise to also purchase a tubing bender, unless you have something already. Without a bender, you will kink the tubing trying to make your bends. You'll also need a small tubing cutter.

For brazing the brakeline the best solder to use is Silver solder. It can be purchased 2 ways, in a coil, or in a pack of 5 sticks, get the sticks, easier to handle and use, and you'll also need flux for silver solder. Go to Airgas.com, they are a welding supply, there are stores nationwide, so there may be a store near you, to purchase the silver solder and the Safety-Silv flux. Silver solder is the best to use for soldering brakeline, because it has a low melting point. The package of Silver rods, and the Safety-Silv flux will run you right around $50.

You'll also need a torch, if you don't already have one. I use MAPP gas. It burns hotter than propane, but can be purchased at the local hardware store for not that much more than a propane kit.
If you buy it in a kit, you should get a bottle, electronic torch head, and igniter for around $30. The electronic torch head is nice, because once you ignite the torch, there's a button on top that will let the torch burn while your finger is not on the trigger.

Measuring and cutting the tube is up to you. There is a lot of trial and error involved if you've never done this before. When brazing two pieces perpendicular to each other, it's best to use a small grinder or Dremel to grind a fishmouth on the open end of the tube. This does 2 things, 1) it helps hold the perpendicular tube onto the cross tube to make it easier to braze, and 2) gives the solder more of an area to fill in and make a solid joint. When you first start brazing tubes together, you may find it easier to use a flat piece of metal to clamp the 2 pieces to be joined. Best thing I can say is go to your local library, and check out a book on beginning brazing, or have a friend that knows what he or she is doing to help you. I taught myself. I knew a little about welding from Metal Shop in High School. Once you get your cage brazed up, it'll look ugly, grab a small grinding wheel on your Dremel, lightly grind smooth all your brazed joints, hit it with primer, and the color of your choice, and no one will know the difference!

Good luck, have a sense of humor, and be safe!