Strength is important and with a single piece of wood you always have to worry about the grain. Laminating several pieces of wood together and crossing grain patterns will ensure a very strong stick. You would then need to shape it. Laminate looks very nice in my opinion. I have a store-bought tiller stick
but I have made tillers by laminating. Here are some pics to give you ideas to chew on....
If you decide to go with a store bought stick... I have this one and really like it.
You can put one of these lock boxes in the gunwale...
By adjusting the length of the stick, you can lock your tiller in any position you like. I use it all of the time when I'm single handing the boat and need to go to the mast. If you go with this model, don't forget to buy this little clip...
When not using the stick, you can fold it back on top of the tiller and clip it in place. Very handy.