Well, sometimes you have to man up and grab the "Bull" by the ...oh never mind.
Flashing a wall is really not that difficult. It takes a little time and patience.
-Carefully remove the shingles one full shingle width away from the wall, using a shingle pry bar. Working one shingle at a time break the seal strip on each shingle. You should have a zig zag pattern running up the roof next to the wall as you don't want all the butt joints lining up on top of each other. They should be at least 6" in the stagger.
-Clean the roof of old roofing underlayment and nails.
-Take you skill saw and set it for the depth of the siding and no deeper. Lay it on its edge and from the bottom to the top cut a straight line up the wall. You should be removing about 4" of siding. More about this later.
-Install the new shingles, one at a time over new roof underlayment. Install a piece of step flashing on each shingle as you go up the wall with one nail in the upper corner away from the wall. Apply your mastic as you go. You will get some on you, it's unavoidable.
-When the shingles are complete, take a piece of pressure treated 1x4 and fill in the void you created in the wall. Caulk the edge where the cut was made to the new board. If you made a straight cut, it will be a fine line.
-After the install is complete, prime and paint the new boards to match the siding. I would suggest primming the new trim board on all sides and also the edge you cut on the existing siding.
-Go to a local roofing supply house (not one of the Big Box Stores) and get your shingles, underlayment, flashing, caulk and any advise you need.
AND MOST IMPORTANT, IF YOU ARE NOT COMFORTABLE WORKING ON A ROOF, HIRE A PROFESSIONAL. Falls can permanently injure or kill you and yes more accidents happen on low slope, single story roofs. Never work alone, have a helper present when you are there. And what ever time you think it's going to take to do the repair, double it at least.
WD-40 is great for getting roof cement off you and your tools by the way.