"O'ch chi'n arddwr."
Translation:Were you a gardener.
I'd like to suggest putting a question mark at the end of this sentence.
This kind of question about someone's name or occupation is more usually framed using the emphatic construction, with the thing being emphasised or enquired about being put at the front of the sentence:
- Garddwr o'ch chi? - Were you a gardener?
- Dewi dych chi? - Are you Dewi?