Attach Garage to Existing Wall
I would sketch out your plan to scale with dimensions and provide that drawing to your building department for your permit. I have done exactly what you are doing 3 times. Is your garage going to be totally enclosed? 
If it is the wall needs to be fire rated , this is not that hard removing the siding 2 sheets of Sheetrock with the seams staggered is what it took for me. On the one I added a door directly into the garage it had to have self closing hinges and be fire rated the other 2 had man doors out the back close to a entry door for the house. The best advice I can give is to make sure you use a wide flashing up under the house siding at least 4” up and 8” on top of the roof possibly taller if your wall is on the wind side. 
If the structure is going to remain open you may not need to have a fire rated wall but the ones I did were enclosed. Today any receptacles you put the garage will require GFCI protection even in the ceiling.
If your plan doesn’t meet code they will red line it with a correction unless engineering is required then you will know you need to have it revised and stamped.  I found my basic plan in a book back then laid it out and submitted I think they required a double cripple for the header but other than that it was approved.