Since I wanted to start off with transportable, do-it-yourself armour, we're going to do lamellar armour. This is an old, old technology. We've got examples in bronze, leather, even bone in some cultures. Lamellar is nothing more or less than pieces strung together to form a whole. It can be as ugly as deer shoulderblades drilled and stitched or as beautiful as Samurai battle armour.
When making lamellar, you first need to decide on your shape. I went with basic scale shape seen in history from London to Rome to Byzantium to Siberia to Tokyo to Anchorage.
Now, here is the important part. When you've decided on the shape of your scale, and the pattern you want (links for examples on the bottom), you find the smallest piece of leather you've got that will take that pattern and make your prototype. Cut it out, look at it, fiddle with it, make SURE that is what you want. Then you get a piece of cardboard, metal, wood, what-have-you and you make your stencil. Trace your prototype, then cut it out on the INSIDE of the lines. One of the interesting bits of working with harvested leather is figuring out how to get the most scales for your piece. Depending on the boot, I could get anywhere from ten (for a cheap summer boot) to two dozen for a nice winter boot scales per boot. Trace them out on your leather and cut them out. I've found that chef's scissors work great for this. Might want to ask the cook in the house, or go buy a set just for crafts.
Before we get in a rush, you need to decide what kind of armour you want. Do you want just a vest that plops down over your head? Do you want a suit that is one solid piece with a head-hole that ties in the side? Do you want a suit that fastens in the front? This is all up to you. Browse the internet and find something that looks cool and interesting. Then take you an old t-shirt and put it on. Take a metric TONNE of duct tape and tape that thing all over till it's stiff. Then carefully cut up the back. You've now got a mold of your body. From here you can take cloth, or newspaper or whatever and make a template of what that awesome armour looked like, and how it fits to your body.
Or you can be a dumb-ass like ME, do NO planning and just try and make it fit as you go along. This works better with the vest-over-the-head kind of armour, which is why I picked it. Easy, but a bit restrictive. The amount of work you want to put into it is up to you. But don't be afraid to experiment.