Just a couple of impressions from scanning your post: I'm not sure exactly where you will be getting most of your light. None through the north wall, morning sun through the east wall, and the rest through skylights? Skylights will let through some ambient light, possibly a few minutes of direct sun depending upon the pitch of the roof and the angle of the sun, but the given amount of bright light on any square footprint of gh space (for plants) would be relatively small. Would your HOA object to twinwall polycarbonate for your roofing material? Compared with the expense of shingling and skylights, I think you'd come out way ahead, too. If you let in more light via a twinwall polycarbonate roof, those attic vents won't be enough. You said ~400 square feet...including peak I'm going to assume a 12-foot roof space. 20 x 20 x 12 = 4800 cubic feet. Cooling and airflow is going to be your greatest concern. You're going to need heavy-duty greenhouse exhaust fans, with a combined output of at least 6000 CFM. These will most likely be noisy -- don't know if that'll be a consideration or not. A method to reduce some solar gain is shade cloth, stretched over polycarbonate panels at a distance of about 6" or so. This is something else that might not be looked upon with favor by your HOA. It would have to be secured very tightly to make sure that one of your spring thunderstorms wouldn't carry them into the next county! Achieving the right balance between growing plants and storage is going to be your first hurdle. What you must do right now is decide what you want to grow, and how much space dedicated to that purpose, and then design the greenhouse around that goal. Trying to make a "bright grow space" work, after the fact, almost never produces the results you're looking for. For example, if your plan was to grow plants on the south side of your garage/gh, they wouldn't get enough light because of the wall. Adequate light would only be found in the center and north side. (If this is the case, then the south side could be your pathway to access items in your storage area.) If growing plants is not part of your plan, then forget everything I said above! -Bruce

^^ Easier said than done. You would have to completely redo the one side of the roof and scratch the dormer. Honestly if you did redo the roof like that it would look out of proportion in my opinion. The only easy option is to extend the flat roof. Perhaps remove the dormer and embrace the gable and flat roofs. The dormer in that one little section in the back would look odd. Or, redo the whole roof in that area with a gable similar to the dormer but covering where the current dormer is, the current garage, and the addition.

The front door and double windows are an enclosed front porch so the top level is lower than a window top edge should be. The gutter repair area is from removing an existing metal car port.

Depending on the cost, I intend to do a full-fledged professional conversion of the left half of my 23 ft wide x 20 ft deep garage into a 10 ft wide x 20 ft deep practice space for my very loud drummer husband who currently practices in our aluminum sunroom (bless our neighbors who have put up with him for 15 yrs! & me for having no sunlight entering the back of my house ; ). Most say I'm crazy to do this, but this is probably our forever home, Charleston is a hot market, and I could describe it as a theater room if I ever were to sell. We live in a flood zone so our house is 5 ft high. There are steps leading down to garage which is at ground level. We would begin by framing in half of the garage facade & installing a new single door to replace the current double door. Once that is done we would have the most expensive part: the concrete piers extending from the garage slab floor to support the new floor so it is level with the rest of the house. We are lucky to have a garage with a huge ceiling! Sooo back to the original question, how do I make the exterior look normal? It helps that we have a huge oak tree in front so the driveway is only a few feet long in front of where the new room will be, helping it blend. My concern is merely what will become the dead/negative/blank space. It will just be a wall of nothing but boring vinyl siding 10 ft wide and 8 ft high (see photos/it will be the left side). Thank you all so much!!! Sorry for being so long winded.