Translation:A big car is waiting in front of the stop.
Duo's sentence is correct.
Station = állomás
Bus station = buszállomás
Bus stop = buszmegálló
Can i say "Egy nagy autó vár a megálló előtt"? i thought it that way since the emphasis is on "the big car"
That works too!
Your sentence might put more emphasis on 'egy nagy autó', but not necessarily. The empathic position is always directly in front of the verb and both your sentence and Duo's preferred one have 'egy nagy autó' there. Since in yours it's also in the first position, there might be a bit more emphasis on it, but intonation would have a major role here.
I thought so too. I wrote: In front of the stop a big car is waiting. Wasn't accepted so I reported it.
I translated "... egy nagy autó..." by "One big car" and got corrected. I thought since egy = one (the numeral), it could be used in this context. Is there a reason it's not possible here?