Rhino Stair-Wall Modeling

I have a stair and adjoining wall concept that needs to be turned into a clean, well-organised Rhino 3D model. All I can share for now is a rough sketch and a few reference photos; from those, I want a fully built .3dm file with sensible layers, joined surfaces, and watertight solids so the geometry is ready for section cuts and potential construction drawings later.

The scope is limited to the stairs, the wall they touch, and any immediate trim or stringers that visually tie the two together. No broader interior context is required at this stage. Please keep dimensions and proportions editable, as I may ask for minor tweaks once I see the first pass.

Deliverable
• Rhino 7 (or earlier) .3dm file with clean layers and named groups

Acceptance
• Geometry must be manifold and export correctly to STEP/DWG without errors
• All curves, surfaces, and solids remain parametrically adjustable

If you have recent examples of stair or architectural elements you have modeled in Rhino, a couple of screenshots will help me gauge fit.