Well, years ago I laid down cedar 2x6's and put a 5/4 cedar deck down over a covered roof/deck. Did this in sections so at any time they could be lifted and the roof cleaned underneath. I since moved away but have been back and ten years later everything is peachy keen.

The answer depends entirely on the applicable building code and local amendments so it would help to reveal that information up front; that would help avoid such a wide range of opinions and guessing If the code is the 2015 IRC, R311.7.10.1 describes how a spiral stair can serve as an egress inside and outside of the house. The clear width at and below the handrail must be a min. of 26" and the walk line radius should not be greater than 24.5". Min tread = 6.75"; max riser = 9.5". Min headrooms = 6-6. I suspect the applicable code is different or amended because it apparently limits the area served by a spiral stair to 250 s.f. but in your case that doesn't seem to be a limtation. Are you skeptical of your architect's judgement? He/she at least knows what the applicable code is and no one here does.

Wait! What? - "Framer said the sloping can be done in the tiling process..." Rule #1: Architect Before Builder Rule #2: Architects design structures to maintain safety and code Rule #3: Builders BUILD the structure to the SPECIFICATIONS of the Architect Rule #4: No one alters the plans without the Architect's Signature Rule #5: Do not take structural advice from the guys who swing hammers Rule #6: Do not take design advice from the finishers/painters So...the Elephant in the room is the "Framer said". That's where you stop the build and bring the builder BACK IN to explain how and why a framer was allowed to redesign an Architect's requirement. This is a MASSIVE mess that needs to be stopped RIGHT NOW! You need to hold the Builder to the standards/plans created by the Architect (who must follow code). Don't do anything until your Builder comes in and rebuilds this deck. And please, do NOT take structural/code advice from someone who swings a hammer. Not unless they can show you their Degree in Architecture (and can indicate how their modifications can and will support code requirements).

My comments remain the same. Maybe I should explain further. - A flat roof expressed on any addition to this house would look like an afterthought. If you truly desire a rooftop deck, and want to go to great lengths to minimize this conversion, then you can design the elevations and massing placements to account for a flat, or partially flat, roof to have a cohesive design (and budget and complexity of build will reflect that solution). However, it seems you are just looking for a way to eliminate matching the shingles on the addition and coincidentally a flat roof can be usable for a deck. Note that Certainteed's website currently shows Spanish Tile as a color for Presidential Shake TL. - Where would the stair be placed for this new garage rooftop deck? You show a 13 riser stair leg (turned from the 8 riser stair) in the existing garage. I assumed the 13 riser leg was new for the rooftop, because 13 risers is for an 8' ceiling (and the photo shows only about 4' lower grade in back). Instead if this stair is to replace an existing pull-down attic ladder to access what looks like a 3' high attic storage, it seems a waste of precious floor space in the old garage (not to mention the headroom available at the top of stair where it is placed). -"Light+ventilation" is a code requirement of 8% glazing/4% opening for habitable areas which the garage conversion requires, so moving the old windows to the old garage door might be inadequate from an eyeball test. - Along the back you will have a tall stem wall and need to infill the foundation because of the slope, so the jogs in the back by the "added closet" and outside stair are inefficient to build and with this layout don't appear to add to the design. - The existing sewer line from the house to the street is at a certain location and fixed depth based on that location. If you want to connect the new bath, the bath line will arrive at a certain fixed depth based on how far away the tie-in is. That will be problematic if it arrives lower. Also whether that tie-in is allowed outside the footprint of the house. May or may not be an issue, but usually when beginning planning an addition you locate plumbing as close to the existing house as possible to minimize potential issues until you can investigate further. - Bumping the addition completely to the side brings up property limitations (setback, easement, FAR, etc). Driveway access brings up routes to enter or back out of a garage. Size of driveway to remain/new brings up impervious surface limitations. These all should be verified first. It may be best to hire an architect or professional designer to help you evaluate options, space needs, feasibility, and costs.