If you've never made anything out of papercraft before, I suggest you look elsewhere Papercraft Museum and make something out of paper, it takes a significant amount of more effort (and time) to work with aluminium.
Step 1: Flattening Aluminium Cans
The method for flattening the cans that I've found works best is to use a sandwich maker (an old one, don't ruin your good sandwich maker!!). Before turning it on, lay down a piece of baking paper on the bottom, put about 4 cans in, then add another layer of baking paper on the top (this should help prevent at least a little bit of damage to the sandwich maker).
Hold the cans down flat as you close the lid, once you've done that, turn the sandwich maker on.
I haven't fully experimented with getting the best efficiency here, but I left it on for 10 minutes with 4 cans in there, then turned it off and let it cool before I opened it.
Taadaa! Flat cans!
Other methods I have tried are:
* Ironing (Does nothing)
* Ironing and bending at the same time. This method works, but you end up with your piece looking a little bit bent as it's hard to get it as flat as you would in a sandwich maker.
* Clamping it between 2 pieces of wood. This does absolutely nothing, if you leave it for a day or a week, they bend right back to their natural shape.
It seems like heat is very important in getting these things to stay flat.
Step 2: Cutting the Sheets
Also, because the cans are way thicker than paper, you'll end up with parts that will fall short because the thickness of the paper messes it up. I just dealt with it as I went and it may have resulted in a less than perfect final product, the design would probably have to be altered to give a bit of room in some corners to account for the extra thickness.
Using a knife is practically useless, you just can't drag a knife through aluminium like you can through paper.
Scissors on the other hand are brilliant, it's just like cutting through paper. The only issue is the end of the scissors can cause the aluminium to bend a bit. To counter this, I use a knife to piece the corners, then use the scissors to cut up to them. It's not perfect but does the trick nicely.
You should also score the pieces using whatever you normally use to score, I use a thing that's a bit like a needle on the end of a knife handle.
Folding is pretty simple, just do as you normally do. Be careful about bending too much though, as the metal will weaken the more you bend it!
Step 3: Gluing
This part is going to take the majority of your time, I suggest you glue 1-2 pieces at a time, put the contact cement on them, let them sit the full 20 minutes, then push together (hold for ~10 seconds or so to make sure it's solid) before moving onto gluing 2 more pieces. Get a movie out, play some games... It'll take a while.
The contact cement wasn't the greatest however, as if the metal is trying to flex against the glue, it'll pull itself apart unless you sit there holding it for at least 30 seconds, even then it doesn't feel as strong as one would hope.
I didn't end up trying Epoxy however, so that would be a good thing to experiment with.
Other glues I tried:
* Aleene's Original Tacky Glue (the metal surface was too shiny for the glue to stick once it dried). This is the glue of Papercrafting gods that I had to import from the US to Australia. It's very similar to PVA/Wood Glue, just slightly tackier making it awesome for papercraft. Just not for... Aluminiumcraft :P
* "Hobby Cement" - Same deal as the Tacky Glue above
* Bostik Multi Bond - Same deal as above, it just can't stick to the metal as well as it should.