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

I should have been more clear... the house was built in 1959, but has had several upgrades during the ensuing 60 years. The two car garage that is attached to the house had been converted to a room before we ever bought the house (20+ years ago.) Originally the driveway came from the east (front of house) , but was moved some time in the past to the north. We have never used the space for our cars. During some remodeling in the past, the garage doors on the north were removed and a large window installed, as well as a door out to the driveway area. Two windows were put in on the east. There is a door to the west that has a big step up to the patio and deck. A wall AC/heating unit was installed. There is no direct entry into the house. We have primarily used this space as storage that we are now clearing out. Currently, I don't have a TV room or den, or any place that will comfortably allow family and grandchildren to gather, other than outside on the deck, which is not very comfortable in Texas summers or during the winter. The room itself is about 19'X 24', with the raised area, 15' X 4'4" on the west side. My plan, after talking with contractor, is to extend the raised area another almost 10" into the room to give more space for a some storage cabinets and a work counter, and another 4' so it meets the south wall. That will give me a raised area of about 19' X 5'2", roughly. I'm getting the appropriate permits and using licensed contractors, so I'm not trying to cobble something that will be unlivable. I plan to stay in this house another 30 years at least. However, having this space will bring me great joy, as I really don't have an entertainment area for my grandchildren at this time. My biggest question is a design one about the flooring. Since I have that raised area, what would be a good way to transition the floor? I would like LVP, but wonder about that lip from the raised area to the "main' floor. It actually is about 3". Rather than LVP on the raised area, would another flooring be better? The previous owners had put down an indoor/outdoor carpet which wrapped down over the edge. I don't love it. My current budget to get permits for electric, remove the fluorescent lights and install additional lighting, remove the indoor/outdoor carpeting, replace the door and framing on the driveway side, extend the raised area and install the flooring is about $9000.

The door by the laundry in the first one would lead to a small courtyard in our side yard. We don’t need access to it but it’s kind of unused side yard space otherwise, so we could link to it and turn it into a nicer area. We do have a powder room in the other part of the house but it would be nice if this one could also be accessed by the main area (doesn’t need to be in the nursery). We have a king size bed, and ideally the nursery could eventually hold at least a full size bed if needed. The French doors lead to our backyard and we want them to be accessible without being in the master. The connection to the house is on the side of the kitchen by the pantry. It could potentially move east (up in the picture) but we’d have to reconfigure the pantry and a closet in the existing house. I’ll draw up another picture that shows what’s inside when I get back from vacation next weekend. Thank you for your help!

I can't tell you how much I dislike garages that are in my face in front of an entry to make the front of the house all garage as the first thing you see. But that said I do not like bedrooms above garages either. A garage is not living space so you will need to dempolish the garage and then build an addition just like any other addition. Can you do what you want where you live there are often rules about sq footage of living space in proportion o the lot. As for cost that can only be decided after getting all the info you need and then quotes from contractors in your area. IMO you also need an architect since IMO additions are best when they look like they have always been there