How to support loft floor if I fit new windows (Ed.)

[REG_ibson]

Hi, I am replacing the back of the house with new glazing.
If I wanted to add a floor in the attic at a later date, how would I support the new floor on the wall plate?

The diagram below shows the existing ceiling rafters and not a new support for any floor that would be added to the roof space.

Would I simply have to rely on the support offered by existing walls within the property and not be able to rest any new timbers onto the wall plate?

 

[^woody^]

It all depends on the required depth of the joists. Otherwise beams to support the new floor