Learn Italian: Nessuno vuole una camera così inadeguata come questa. - Nobody wants a room as inadequate as this one.

The prefix in- is added to adjectives to mean "not", just like in English. Here, it attaches to adeguata (adequate) to create inadeguata (inadequate). Because it describes the feminine singular noun camera, the whole word still ends in -a.

Why is there no non before the verb since the sentence uses nessuno?

When negative words like nessuno (nobody) or niente (nothing) come before the verb, Italian does not use non. You only use a double negative if the negative word comes after the verb (for example, if the sentence were: Non vuole questa camera nessuno).

How does the così ... come structure work here?

This is a comparison of equality, meaning "as [adjective] as" in English. You put così before the adjective and come before the noun you are comparing it to. It literally translates to "so inadequate like this one".

Why does the sentence end with questa instead of questo?

Questa means "this one" and is acting as a pronoun here. It refers back to una camera (a room), which is feminine singular, so the pronoun must also be feminine singular to match.