In truth, the new stadium is not nearly as high-tech as Madrid's. But it is considerably bigger and also better looking imo.
A lot will depend on how well the roof is constructed. It doesn't have to be fully covered at all, looking at Barcelona weather. 360 huge screens are not suitable for a lightweight roof like the one Camp Nou is gonna have. It's much more a question of added weight than cost.
Based on online sources, the roof is gonna be mostly built using tensile-structure architecture. With cables, some light steel beams in some key areas, and generally using lightweight materials. It's not gonna be a mall-style stadium like some of the others in Europe (with huge metal and concrete structures). The cost of a full-on metal roof would have been insane looking at the size of the thing. Would have nearly doubled the price probably.