bits of paper
Well back when I was 12/13 with my friends, we used to just get lots of little bits of paper and write each letter of the alphabet on each bit of paper and arrange it into a big circle. I've also used the letters from the game 'scrabble' in the past..
You can also add numbers, and of course yes/no too. Hello and goodbye are really important for opening and closing the session properly.
For the planchette you could use a glass tumbler.
I used to have a really big chalk board and that was great because it meant I could just write the letters on with chalk and they wouldn't get pushed around by the planchette... because with all those bits of paper.. a gust of wind is going to leave you a bit screwed!
I made one a couple of years back for a friend, cut out some wood, got some of those transfer letters you can get from stationery/art shops for like 99p and it didn't take long to make at all.
transfer of energy
A prefab board appeared at the coffeeshop I used to own with a friend. (Long story, maybe another time, but it seemed that we were to have one, so I kept it). I used it with a different friend and it seemed slow, or sludgy or something.
We talked about making one, thinking about the transfer of energy that occurs when you put time into a project. So, one day, on an apparent whim it occurred to me to use the back of the prefab board for the homemade version and got busy on it. (I just used permanent marker to mark the letters, numbers, y/n, HELLO, GOODBYE, and a few symbols we added to help clarify the communications). I covered the front of the prefab to make it a back (I thought that leaving it as it was could result in some uninvited guests and I want to avoid that!).
We used a small round glass ashtray as a planchette. It worked well, on the prefab and the home made version.
It is important that the board you use to make your ouija board is smooth, not coarse. ALSO- YOUR FRAME OF MIND WHILE MAKING IT IS CRUCIAL> That means not when you are sad, angry or other wise unstable, same goes for when you use it!