Planning for future roof access after wraparound & loft conversion on mid-terrace

[NCXo82ike]

Hi, I couldn't find an answer to this by searching but suspect BH may have good advice. 

We're planning a wraparound extension and L-shaped dormer to a mid-terrace house (as attached) and I want to pre-empt future roof access.

I don't want to rely on the neighbours' side return for access. A future owner will inevitably build there.

For the neighbours' amenity, planning will only let us have a pitched roof on the wrapround extension rather than flat, insisting on a pitched design. We need to maximise internal height relative to the allowed party wall height and probably will have a box/hidden gutter here. The left slope is 25 degrees, the right 9.5. Roofing will be EPDM or GRP.

We'll have skylights in the extension, one in the loft above the (otherwise very dingy) stairwell, and perhaps one in the bathroom on the outrigger of the loft (although I'm concerned about solar gain from this).

The front access of the house is 6m to the soffit with a 35 degree roof- this could be used to access the loft skylight but the rear loft window would still be a problem.

 

I want to make sure we can clean the extension skylights, 3x 1st floor windows, 2x loft windows and 1(/2)x loft skylight. I also want to consider roof maintenance and gutter cleaning. There's a chance I'll get solar panels put on the loft too, also needed cleaning.

I spoke to some window cleaners who seemed very gung who about this but I'm concerned they might actually struggle. And other trades with heavier tools/materials might think differently.

 

Grateful for thoughts on the following please:

1. Does anyone ever build in treads to a roof e.g. GRP, to allow walking along a slope as we have on the left, or even some sort of lugs a ladder could be braced against?
2. Would an opening skylight in the loft bathroom be the most sensible way to clean the loft skylight(s)?
3. Is there  a value to pre-installing something high up that a ladder can be secured too- like a eyelet/attachment point.
4. Am I just underestimating other people's ability to work at heights?

 

Edited March 6 by NCXo82ike