The best way to say "você está com calor" in English?

Sim!

Esta é a melhor maneira; mormente quando se conhece o contexto em que a frase está inserida. "Are you hot?" antagoniza "Are you cold?"

> Are you hot? ... Yes, I am too hot!
> Are you cold? ... No, I am warm!

I would state "yes, I am feeling hot" (and sweaty, depending on the wheater being stuffy, etc).
Asking "are you hot?" could lead to some ambiguity, there was even an American TV show named Are you hot? - The search for the Sexiest People. There is an entry on Wikipedia about that show.
So I would favor the form "are you feeling hot?" (asking if you feel at the time of asking).

Do you feel hot when you catch a cold? - asking of previous/past times, though is not unusual the usage at the time of asking, many people will ask that way.

One more instance is the article on a site "How do people deal with sweating and 'feeling hot' at high altitude climbs", that explains the ""feeling hot" some climbers felt at high altitudes, to the point of even removing (or trying to remove) their own protective clothes!

Ref. dictionary.cambridge