Fireplaces, Heating Stoves, Flues and Chimneys - stove pipe question

I live in Maryalnd and have a 3 car garage / workshop that i want to install a wood burning stove in. A friend has given me an old Ashley wood burner stove, but my question is the most inexpensive way to run the stove pipe. The stove has a 6 inch opening in the back of the stove (might be 8"). I was wanting to place the stove in the middle of the back wall and come directly out of the stove with a 90. Then straight up through the roof. I have seen single wall and double wall pipe. I would like to use single wall pipe for cost and the radiant heat. It would be about 14' of pipe to the roof line then a couple more on the outside. My biggest concern is going through the roof. I dont know how big to cut the hole in the roof so that the plywood would not get to warm from the pipe and how far of the back wall the stove needs to be. Any help or other ideas would be greatly appreciated.