I must say I've never had to make my own as I have been lucky enough to find cheap ones at boot sales etc, but I am usually pretty good at making things from scrap! Its a good challenge to think how to overcome little obsticles which is why I like crafting so much!
I would use thick round sewing elastic to act as the springs that grip the plate tightly (unless you have a load of small springs laying aorund?). For the grips you will need to make something that won't scratch the edge of your plate but that won't flex and drop it either! I would have a rummage in the shed for some strong wire or similar and cut and bend it into simple hooks (using pliers and a vice) with a loop at the other end for the elastic to be tied to. You will also need a couple of longer straight bars, with a knotch for the hanging point in the centre, and hooks at either end for the elastic again that sit across the back. Make sure you have a picture or an example of a finished real plate holder to follow!
When your hooks & bars are complete, paint them with thick white gloss paint to neaten them up and protect the plate, leave to dry and finish with a coat of PVA glue as it has a nice tough springy surface when dry and will help cushion against the wire surface in case the paint chips off.
You need to test the tension before cutting and attaching your elastic, so I suggest sitting with the plate and materials on your bed in case you drop your precious plate! Tie the elastic into place tightly and check its grip by attaching to the plate an holding and bouncing in the air. Adjust until you are happy with it, then trim off the ends! I also recommend singeing the knots on your elastic with a lighters flame once you've finished to stop them from working themselves loose!
Hopefully I've made sense, it would be good to know how you get on! I have a fairly new website dedicated to arts and crafts projects including budget home projects so feel free to have a look at www.craftyfox.webs.com! If yours turns out well it would be nice to be able to add it to the tutorials on the site with pictures, maybe we could start a new trend!
Sarah (craftyfox) x