No lawyer but company's would have the right if you are reproducing and they feel you are watering down the value in their name and product.
The first part of your question I presume is ,Is it forbidden to create for non profit.
If it was for your self and a one off I think it highly unlikely they are coming after someone over one car, but the risk is there in reality.
I have always wondered about all the P4 replicas out there, and Ferrari have not tracked them down like other models that have been copied in the past,maybe it is because 3-4 only exist so everybody knows and its not seen as a threat by Ferrari.
Jim