Minimum size wood for stud work to level wall? - Tile Advice

[highpeakrider]

Hello

I have an external hollow block wall which is really brittle and uneven.
Although I will loose some room size I was thinking of facing it with a stud wall to ensure its square then glueing and screwing 6mm nomoreply.
Tiles are 500 x 250 ceramic, what's the view on the minimum size wood I could use in the construction?

 

[Tile Marble Granite]

Did you manage to fix that wall? If not, you can render the wall then waterproof it, timber speaking: you can go to your local timber store and find what you are looking for. I miss those days!