Mid terrace yard multi wall poly carb roof query

[Gavin583]

Hello

 

2 storey mid terrace property with rear extension both side (one side is neighbours) of the rear yard. Planning on putting a roof on it and using 10 or 16mm multi wall poly carb sheet.

 

Looking for advice/confirmation my plan is good enough as not worried about weight of the poly carb sheet just that the structure would be strong enough as I will need to stand on the poly sheet to fix it in place, flashing etc 

 

4200 long 1800 wide approx, all 3 walls are dashed

Plan a 15-20 degree fall along the 4200 length.

6*2 on both 4200 walls fixed with concrete screws 

6*2 on the 1800 wall with concrete screws 

Also notch both (might be overkill since fixing to the wall?)

Another 6*2 running down the middle at 900 centre notched and screwed to 1800 wall plate and screwed Into 1800 6*2 at open end

Add supports/noggins at 600 centres connecting all 3 6*2

Put the multi wall poly carb on top, taped screwed, tape flashing and sealant along the dashed walls.

 

Does this seem overkill with the centre 6*2? 

1800 seems large without it.

6*2 thick enough? 2 inch or 47mm doesn't seem like a lot of holding?

 

Any better ways of doing I'm happy to listen