If you decide on a shallow pitch porch roof use 2 by 6 foot rafters.
How to attach roof trusses to wall.
A ledger is a horizontal board that is attached to the top of the wall.
Install the second truss in the same way 24 inches along the wall from the first truss.
Nail a long 2 by 4 to the underside of the rafter on the opposite side of the truss from your diagonal brace so that it extends along the length of the roof passing through the second truss.
Use bracing to keep the trusses in place as you work your way across.
The ledger is needed to properly attach the perpendicular roof trusses to the top of the structure.
Use screws to secure the rafter to the sill plate.
As with rafter style roofs toenailing is one of the most common ways of attaching a truss style roof to a wall plate.
Roof trusses are prefabricated wooden roof members that combine the rafter and ceiling joists of conventional framing into one structural piece.
Joist hangers can help you mount each rafter to the house.
Walls that are constructed of concrete block that need to be covered with a roof will require the use of a ledger.
Some building codes around the country require the use of a hurricane tie also shown above to add extra reinforcement for holding down roof trusses in the event of very strong winds.
Although a roof truss may be heavier and more difficult to maneuver onto the top of the building than conventional framing lumber once there it can easily be slid into position and secured.
Another great way of attaching the truss end to the top wall plate is to use a simpson fastener shown in the picture above which you can find at your local lumber store.
After attaching your truss make sure it is plumb before proceeding to the second one.
After setting the second truss in the same manner workers attach a ridge beam to the peak of both trusses.