A free standing roof can be built over a deck paved patio or concrete pad.
Roof on a deck built on deck bloks.
Installing a porch roof over an existing deck is usually not recommended unless the deck was originally designed to support a future porch.
For corners deck blocks are built to accommodate 90 degree angles.
If your deck has a gap between it and your house this might not be a problem as you can simply build a stand alone deck cover.
If it is next to a house or structure it should be secured to the siding or roof of that structure as well to keep it stable through high winds and lashing rains.
Because they are not recessed in the ground deck blocks keep your wood off the ground and prevent the problems that occur from columns standing in water for long periods.
Lay out the concrete pier blocks into six columns and three rows.
Typical decks are designed to support 55 psf lbs per square foot.
Porch decks require 25 additional psf for roof loads for a total of 80 psf.
However many decks are right next to the back of your house which raises a few issues.
A 12 by 8 foot freestanding deck requires no sawing or hammering with a simple ladder frame and pier blocks.
Joining a home made roof to your existing roof might require a level of expertise that you don t really have.
By placing the deck blocks carefully at the outset a deck can be quickly assembled in a matter of hours.
Several commercial waterproof deck systems are available to create a dry space under a deck but rune stactic of adding a roof to a deck seems to be just as effective.