Help with building a shed

by Colin the Shed building noob

So, I've gotten to the point of having the base of the shed built and the walls prefabricated (I built them and have them ready for installation).

It's a 12 x 8 shed. I used 2 x 6 x 8's for the base, spaced 12" apart. Once that was done, I put roughly 5-6" of 3/4 crushed stone down, and then positioned the base until both straight and level. The floor was then put on (5/8" plywood tongue and groove). next the walls will be put up. Here is where I need suggestions.

I have the walls built and spaced in the openings for the windows. However, I have not completed the 4th wall where the door will be installed. I need to leave a space for the doors. This is an exterior storage/work shed. Over the next year or so, I will add a work bench, get electric installed and organize the interior for extensive and organized storage (lawnmower, weedeater, lawn and garden tools, gazebo tarps etc.). I realize some of the items are heavy and wider than a standard door, so I would like to leave the opening large enough so I don't have to struggle to get stuff in and out. Does anyone have a suggestion on how big an opening I should leave?

Next step will be the roof trusses. I am building a 4:1 (4/12 pitch) based on an 8ft width with a 1 ft overhang (per side). The centre supports will be 20" on the trusses. Does anyone have a formula to determine the angles I need to cut for the trusses both where they connect at the top and where they will connect to the supporting 2 x 4 x 10"?