Reaplcing existing single skin wall with cavity block walls

[alcorn6281]

I have an annex with a 6m long brick wall, 2m in height and as a section of the wall requires complete repair work and I am thinking about renovating the annex I was trying to think of a way to create a cavity wall. My best plan is to remove the concrete floor inside the annex and create footings on the inside to accomodate the aerated blocks, creating the internal cavity wall skin, this way it would support the roof and mean the inside of the annex isn't exposed to the weather. Next step would be to remove the brick wall, remove any possible footings that may have been there replacing with new footings and combine both with rebar etc and rebuild the aerated block wall.
Im a novice at this type of work, I don't plan on doing it myself but I would appreciate any suggestions or advice on my design concept, I have read what I can on building regulations for my area and building techniques from this site and others and this is what I came up with. The only reason I am not removing the brick wall and doing everything at once is simply that it will cost more than I have at present and it will leave my property unsecure.

[welsh brickie]

In this situation I would build a temporary partition wall inside the property and seal it against the elements and also to support the roof.Then remove the single skin wall to the foundation level,Cut back the concrete floor,and remove the foundation,Then lay a wider thicker foundation and build a cavity wall.