Mahogany is a good choice for the 3 lengths of hardwood. This will allow the tripod to last for many years.
The same applies to the screws, bolt, washers and hinge. Get these is brass to eliminate rust problems. The length of the 3 pieces of wood is your choice but I would recommend these measurements. 1.75m x 5cm x 1cm The bolt needs to be long enough to pass through all 3 pieces of wood, 3 washers and the hinge.
Drill a hole 20cm from the top of two of the pieces of wood. Make the hole wide enough for the bolt. Drill a hole the same size in one side of the hinge. Assemble as shown in the diagram. Note how the hinge is fitted below.
Having made sure the hinge opens the correct way, secure the third piece of wood with the brass screws, as show. You may wish to make the length of the third piece of wood a little shorter to suit your needs.
Tripods For Sale