Now it says "How much is for the largest room?" I think it should be "How much is the largest room?" or "How much is it for the largest room?"

What is the price of the largest room ?

As far as I can tell, this is the only English translation accepted by Duolingo.
IMHO this is not correct English.
I think the translation should be something like this :

How much is the largest room ?
How much for the largest room ?
What is the price of the largest room ?