Is it pica, or is it normal to crave nail polish, paint or permanent markers?

Possibly Pica. I am not sure from your question, but when you use the word "crave" to indicate that you ingest these items, then pica is a definite possibility. However, if you are saying that you "crave" these odors, then you are not referring to pica. Problems with pica requires the actual ingestion of items that would be considered inedible. If you are doing this, then it would be important to get evaluated.
Pica. Cravings for, active consumption of, non-nutritive substances for > 1 month, not socially sanctioned, & developmentally inappropriate, is pica. This should be evaluated by a medical professional.