I'm planning to cosplay Electra from Starlight Express.
I've got the skates and unitard sorted out, but the hard part is going to be the various plates and pads. Some of them I can so with regular skating gear, but the ones on the shoulders legs and lower arms are giving me trouble.

Any recommendations on what materials I should use would be appreciated.

Edit: Please bear in mind that I'll have to spend all day skating in this costume, so nothing too heavy or restrictive.

Depending on your skill level thick craft foam is easy to work with and can give some pretty good result with some suitable paint and a bit of heat-work! ^^ Reckon it could work well for those armour parts! ^^

Eva foam or plastezote are good as you can heat form them. Probably using a thin foam is best so you can layer it and get the various detailing. you'll probably get quite warm by the end of the day, but it shouldn't restrict your movement too much for skating.

If you're wearing this to any conventions, you might want to sort out shoes since you're usually not allowed to skate - at least certainly not inside.

Best of luck with it

Hmm, how's the durability on the foam?
I don't want a single tumble or collision to ruin the costume.

You could try using expansion foam over a cardboard base? I'm not entirely sure on the durability - but it's lightweight and not too restrictive.

Also - SO much love for you cosplaying starlight <3

EVA foam's pretty durable, I've made entire armours out of it before (example http://www.cosplayisland.co.uk/costume/view/33814)

Actually I think your main concern is how you will attach those pieces to the costume because if you glue them, when you move around the glue will get pulled on and bits will fall off. Velcro should work but might be best if you find out how the original was put together and get some ideas from that.

I've got a general guide on making this sort of thing here in case you're interested: https://www.coscraft.co.uk/blog/?p=206

Thank you.
Now I just need to learn the dance routine, and maybe find some people to play Krupp and Joule...