The minimum pitch for a standing seam metal roof is 1 4 or 3 inches rise to 12 inches run.
Pitched roof under deck.
The minimum pitch for shingles is 1 6 which is equivalent to 4 inches rise to 24 inches run.
Installing a porch roof over an existing deck is usually not recommended unless the deck was originally designed to support a future porch.
First mark all the purlin locations on the deck joists.
Porch decks require 25 additional psf for roof loads for a total of 80 psf.
Instead a pair of beams rest on supports called sill plates to create a frame for the deck.
Then stretch a string between them.
If the span under your deck is 12 ft for example the purlin at the outer end of the deck should be 3 in.
For those who desire a bit more shade and privacy while soaking up the rays however a deck roof may be in order.
Centers supported by a beam and a ledger as on most decks.
Install the purlin along the house and the outer purlin.
A deck on a sloped roof requires a different approach to the framing underneath the joists.
Once you have your beams in place everything above them joists deck boards balusters and handrails is the same as for any other deck.
Typical decks are designed to support 55 psf lbs per square foot.
Whenever i install decking over a roof i make sure the framing is structurally sound and properly pitched to drain water.
The project illustrated here was a complete teardown and rebuild so i framed the roof with 2x8s spaced on 16 in.