Solid wood vs Laminated
A laminated tiller is not "far stronger" than solid wood in and of itself. There are a lot of factors to be considered. One of the main reasons that most tillers are laminated is because of shape. If you were to draw the shape of your tiller on a piece of paper with a bunch of parallel lines (to simiulate the grain of a piece of wood) you would probably find that at some point your tiller is curved and will cross the lines at a point where the grain becomes very short. That is your weak point. Laminating a tiller allows the the grain to follow along the curve and be strong for the entire length. The folks who used wheelbarrow handles don't have a bad idea. The wood used is straight grained and also straight so that there is good strength everywhere. If your shape allows the grain to extend all the way along the tiller solid will be fine. If not, you will need a laminated one. BTW an all Ash tiller will be better than an Ash/Mahogany one as Ash has better bending properties but it doesn't look as good. As far as making one yourself you need to have some knowledge of what you're working with. It can be difficult to make the form to bend the strips so that you have good contact on all joints. Personally I like Weldwood for something like this as it has less creep than epoxy but if your joints are less than perfect epoxy will work also.