Took me a while to figure out. Talk to Livia (woman in your house that isn't a servant) and select "Parties" the conversation should lead to her asking for a private dinner. Buy red wine and high grade food for the two of them. She will mention how she misses good quality food. This will unlock the Field location on the map. You can then buy a plot (there are nine plots available). In the plot of land you can plant a field of grain / vegetables, a vineyard, fruit trees OR build a coop or pen (coop for the hen, pen for the cow).
I recommend you have a hammer for the building process. It will require wood to build as well. After you must place three chickens in it.