Heya. As requested, I've begun to put together some basic tutorials on the props/replicas I've built. I'll give as much description as I think is worthy, and as always- give me a shout to ask questions or opinions.
This build is a mixed media one-off/original.
It starts with finding an image of the prop and either hand-copying it (as I often do) or having it printed out. I like to put my hand to things, and sometimes that means a hand-drawn template/pattern can be a great way to gear my brain to what's to come. Then again, sometimes less work is a great thing, too. If you're new to prop building go simple.
The Kingdom Keyblade is a pretty simple shape- this is no Gunblade or crazy build. We're talking about a handle, a central body, the key end, and a key chain and charm. Using your template or drawing by hand, cut out and trace the pattern onto a piece of plywood or other for your handles and cut them out with a jigsaw. Take your time and pay attention to your line. Do the same for the charm and the key end.
For the main body choose a length of 1 ½ inch PVC pipe and cut it to your preferred length. I usually range from 37-40 inches for most keyblades. Working with a rotary tool like a dremel, sandpaper, and bondo (auto body filler available at any auto store), clean up your handle, key end, and charm edges, fix any cosmetic boo-boos that haven't been already sanded out, and then then fit them to your PVC pipe. Use your template to help guide you.
Scuff/sand your materials at the contact points. Paying close attention to keeping things straight, glue your handles and key end to the PVC. OMG, there's a keyblade! If you find out later that it's crooked and you have the time- take it off and get it straight- you'll be glad you did.
For the rounded butt on the end I used bondo to slowly build up the shape until I had what I wanted. Take it slow. You can always add more, but it's harder to take it away. When using bondo- particularly when sanding anything, wear a good dust mask.
The key chain is a u-bolt, chain, snap hook and charm with a ring from a key chain. Use the u-bolt to mark where your holes should go and then use a drill to make small 'pilot' holes. This will allow you to see if they're in the right spot, and also keep your bondo from breaking away from the edges of your holes. Move from your pilot hole to larger bits until you reach the size for your u-bolt. Hook everything up, and glue in your u-bolt.
Now for paint. I like acrylics because they're water based and easy to use. Often I airbrush now, but there are still some effects and texture that only a brush can give. A bomb can or spray paint can be used. Enamel provides an instant shine. I use whatever I have at hand most often for a mixed media build. Use painter's tape (low-adhesion) and paper to protect the prop from unwanted paint- it's how I ended up with a clean gold-blue-silver edge. With a brush this isn't a problem.
That's the basic rundown. There's a lot of work and thought in between there- but I can't give you that. Oooh, I got all zen there for a moment! Give it a shot. YOU CAN DO IT!
Be good to you.