Locating and mounting the ledger is normally a fairly easy process.
Shed roof attached to house.
If the outside edge is 8 feet high and the area being covered is 15 feet attach the shed roof addition at least 9 feet 3 inches above the level of the porch or other area being roofed or 10 feet 6 inches for a 2 pitch.
The ledger typically a 2 by 6 is usually designed to hold one end of the patio roof rafters.
Work from the height of the outside of the new shed roof.
You save one of the walls.
The good and the bad.
However if you choose to build a freestanding shed and use this style of roof you should plan the slope of your roof in such a manner as to slope down from the front to the back of the shed.
You will need to attach the porch rafters to the house roof rafters and replace the roofing and flashing.
If you are tying the shed roof into an existing roof on the house you will need to remove the shingles and sheathing to expose the roof framing.
Shed roof design combines advantages of gable roof and flat roof with beams spanning between two walls one of which is higher than the other one thus creating a slant usually ranging usually ranging from 7 to 35.
Depending very much on specific small house design its proportions and weather conditions of the location.
More often than not attached shed use lean to roofs because they are easier to build and allow water snow and all that stuff to drop easily instead of trooping between the shed roof and your house wall.
Rafters should be attached to the header beam using hurricane ties.
The ledger should be attached before the foundation is built for a deck patio roof posts and other structure.
Here are the main positives of building attached shed instead of a standalone one.