New defense building : the roof

Hi,

I've thought about this idea for a while, hope you'll like it.

I'll be concise : at TH9, you'd unlock a new building called the Roof.
You could only have one, I think two would be OP.

The Roof could be placed on any building you want, it would adapt to the size of the building under it (DE storage - of course, army camp, even Inferno if you'd like).
It wouldn't have a lot of HP, but it's main advantage is it would be immunized to lightning spells.

You could use it to protect your DE storage to avoid zapping, on you centered mortar / air defense...

I don't have a lot of specifications about HP, price, etc. But I hope you'll like the idea :)