"Es sind starke Schuhe."
I'm a native English speaker. I've never heard anyone refer to their shoes as "strong". I can only imagine they mean high quality shoes that won't rip apart easily? Or maybe they mean the shoes smell? (Strong odor coming from the shoes) Regardless of the intended meaning, the sentence is grammatically correct. Maybe "starke Schuhe" can mean something different in German or it doesn't translate well into English.
"starke Schuhe" sounds odd to me. I'd interpret this as "cool shoes". It sounds like teenage slang from the 1970s.
The German for "sturdy shoes" is "feste Schuhe".