I posted a few pics of this in someone else's thread, but I thought I'd start my own now that I can.
You can see all my progress to date here, although some of the parts I've sculpted but not yet cast may need revisiting (the arms): http://www.xrobots.co.uk/Iron Mancostume/
It's all sculpted in Klean Klay and cast in Aqua Resin, it's not 100% movie accurate, but I have more fun without worrying too much about that ;-)
My current work is on the legs. I'm using one sculpt to make both legs, which when made in Aqua Resin will then have their upper contours cut differently, and the outer thigh part will be made separately and stuck onto each to make the left and right leg. Here's the leg sculpt which is pretty final:
And the chest plate, more on that at the link above: