As promised, I dug out the pics, I'm just afraid there weren't as many left by my photo-eating-cam as I thought there was.
So, basically grabbed a piece of paper and drew my naked foot on it. You can also do this with shoes on. Draw the shape off, then extend it in how big you feel the correct size is.
Mine is 35 cm long for example and on the thickest place it's 34 cm broad, and I choose a loose tear shape, because that's what they seem to have.
I put this on thin cardboard as this was just going to be the base and 'prototype' for my Protoman (XD) / Blues foot.
Next I cut a broad stripe of cardboard, that should be long enough to go all along the edge of the bottom shape. If it doesn't (like in my case) just make a second stripe and and tape them together, so they overlap a bit.
Fix it with tape to the bottom.
Now you'll start shaping the whole thing round, like the shoe of the robots is, by making small cuts into the shoe and cuttin pieces out. Start out with with cutting in and overlapping the parts to see what effect taking how much away will be. Mark it if you fear you might not be able to cut it correctly.
Tape it together once you cut it out.
I tried taking the same amount off of both sides of the shoe, so it would be pretty regular.
=> Result of what your prototype shoud look like:
Thought I do suggest, that you make the front part a bit higher. Tape cardboard you cut away earlier in to adjust correctly.
Try standing and moving in it. If it's comfy, it's good if you are constantly bumping into the edge at the front or back, you might want to shorten it a bit.
Pretty much the same for the actuall leg, thought you should try to make certain the upper back is in the back of your knee and that it goes down enough to cover your natural ankle. You can always cut it shorter if it ends up too long.
Next comes the 'hard' part. Emotionally anyway.
You got both correct and comfy?
Now grab you scissors or cutter and cut them appart. -> No, I'm not joking.
You'll process as follows:
First, cut the bottom of the shoe off.
Then you'll cut the shoe in exact halfes at the backside and front. Grab one half and start trying to place it FLAT on the floor. Since you should have shaped it round, you'll have to make small cuts (most likely on the top, where you cut pieces out and taped them together). If you made MANY cuts before, you can try spreading them out equally with longer cuts. If you mess up, just tape it together again.
I recommend leaving the area out where you'll connect the shoe to the leg => ankle area.
Repeate the same process you did with the shoe with the leg.
I used those three patterns to make my robo-legs out of hard cardboard.
1 x bottom + 2 x shoe pattern (don't forget to paint them on the cardboard mirrored, so you have the correct side inside later) + 2 x leg pattern => 1 shoe.
If you gave the bottom part a certain direction at the tip, make sure you do not make two left or two right shoes
After cutting out the shapes from cardboard, I carefully hot glued them together (and still burned mysef a good couple of times). Having someone help you pressing the halfes together really DOES help.
Next I covered the whole things with wooden glue, by smearing a good amount on per hand, making it create good layer.
Make sure the shoe & leg are in the correct shape already, because once the glue hardens it WILL hold the way it dried. It also makes the surface smooth and shiney and more hard.
You can pappermasche it too, for additional hold. I have to admit if I had the time and the knowledge I have now, I'd have placed paper stripes along the upper and lower edes. They can turn out a bit sharp and well, in my case you can see that it's cardboard if you look at the top of the knee-part.
I'm hoping to still hotglue a wide, but thin piece of cardboard on the inside, below knee high, to put through a broad rubber band with closing inside, to give additional hold to it.
Afterwards I spray painted them with car spray paint and well, this is pretty much what they look like finished:
At this point I'd already carefully drilled holes in and put a screw and female screw (inside) through it. I can now walk pretty normal, thought through the thickness you'll have to walk with spread legs and it will take sometime to get used to such big feet. Take it slow.
Other stuff was done in similar ways:
EDIT: Forgot to mention.
As you can see on the bottom of the shoe, I made the 3D effect with the ... busters I think those are.
I made it by using foam board. First I cut out the bottom twice, then cut the 'hole' in after marking it with ruler (used a small plate as shape) and glued the normal one the one with hole, before glueing it as good as possible IN the shoe.
I should have hotglued them to the cardboard bottom part (which I didn't use in the end) for better stability.
Cover the bottom part and hole with wooden glue, for more stability, then you can spraypaint it in the base color and hand-paint additional colors.
If you want to make them walkable in halls and stuff without risking ruining the bottom and being able to show off the bottom part like I'll be doing, search for anti-slip sheets in transparent color. Best would be to if they were self-sticking. I put wood glue that dried transparent between the sheet and bottom and there are parts where there are still white spots, because the outside dried first, thus not allowing the inside to dry properly ^^°
If you dare, you can use hot glue to stick it together.
Alternately look for anti-slip mats for showers in transparent (but thick, so the color on the bottom will be a bit more pale, but on the other hand you have good hold even on flat surfaces) or in the correct color if you can find it. (red seems pretty impossible)
I also heard, but haven't been able to try, that silikon (like used in bathrooms) also does the trick.