How to build a 24' roof truss?
The type of roof truss design that you show is far from optimal. You should be thinking of something that looks a lot more like the picture below.

 

https://www.selecttrusses.com/truss-calculator/

This design provides a lot better support for the rafters and for the lower chord. You can get the rafters ready made where the metal finger plates are pressed into wood joints from both sides of the rafter assembly. Alternatively you can also easily make your own rafters by cutting plywood pieces that cover each joint that are then glued to the rafter members with construction adhesive and nailed with 8d sinker nails in reasonable quantity. 

Many years ago when I worked on construction jobs we built rafter trusses on site using the plywood, glue and nails assembly technique. We laid out a template on a large flat work space with guide blocks to get all the rafters built to the same dimensions. (Note that the plywood pieces were applied to both sides of the truss and were not necessarily minimal sized. For example we would make pieces shaped like this for a couple of examples.