Consider choosing large and wide area outside your house so the roof truss can be constructed lying down. Once the construction finishes, it is tilted up and placed securely on the roof. You will be required to set up a table saw. Wood truss lumber must also be cut to size. Measure and cut all the lumber at once so it is ready for construction purposes.
Use a 24 foot piece of 2 by4 lumber as the bottom chord of your roof truss. Now consider creating a triangular shape using two 18 feet long pieces of 2 by 4 lumber that overhang bottom edges of the chord about 15 cm and connect at the top peak.
Use a metal gusset to connect the two top chords at the peak. Similarly, bottom ends of the top chords at the bottom chord can also be connected using a metal gusset. Secure the gussets to the wood with 8 penny nails.
Now start preparing two webs at least 8 feet long. These webs are the pieces of 2 by 4 lumber placed between the bottom and top chords. Hammer 16 penny nails in at different angles to connect the peak to the tops of the two webs. Now the bottom chord can be divided into thirds be making a connection between the bottoms of the two webs. Secure the bottom chord to the webs using metal gussets.
Consider creating two more webs both 3-4 feet long. Attach same gussets with the longer webs to the bottoms of these webs. Attach the bottoms of the webs with the centre of the top chords on both sides.