Not finished yet, but have a pic for you where we're at. One thing I really like is the layout my husband did laying two pieces of the decking in the center perpendicular to the house & using 12' decking from center both directions. Eliminated seams. Our deck is pretty basic, pt rectangular ~10' x 24'. We'll have black aluminum railings. We'll be adding steps at the top right of the photo shown that goes to existing concrete steps on that hill. Later, we plan to add a patio or 2nd deck behind the garage for a grill area (top of photo) and a 2nd set of steps directly down to ground level (at opposite end of deck).

The first on the left is a "false saguaro." Look up Pachycereus pringlei, or cardon. They grow quite tall, like the real saguaro, but very slowly.

Essentially until you and two or three contractors walk the house, you don’t know what is involved. Most of us are trying to tell you cost is local. Forty miles from my house to the next city is a different world of cost. The most important comment, one that carries the most weight as far as I am concerned, is Seabornman’s. Only an in-depth, in person assessment of everything that has to be done to make it perfect for you. Do stairs have to move? Is there a massive stone fireplace in the middle of the space you want to have a new kitchen? Is the former living room now a giant master bath? We don’t know until you take possession what you want done so we can’t even guess what it would cost. We’re not mean, but most of us have built and or remodeled several times and we are realistic. Please don’t be angry-you are asking an open ended question. Can it be done? Yes. Should it be done? It will depend on the actual cost at the time you can bid the project and if you decide it will be worth the money to you. Oh dear! I just reread and noticed “ the amazing lot”. The cretins who bought one of our former houses destroyed the beautiful patio, plowed down the strawberries and the asparagus bed, cut down the flowering tree outside the breakfast room-for starters. The husband of one of my neighbors was afraid of snakes so he had every tree removed from their half acre wooded lot.

In general, it is cheaper to build two stories than one, primarily because you have less concrete slab to pour and less roof area to cover. However, I would strongly recommend a one story home if you have the land to do it and plan to retire there. As others said, it depends, but I'll note that from a pure cost perspective, it is typically cheaper to build two stories.