Hi from the south of Tenerife.
The canary Islands are subject to a new law from last year which is a little more permissive in what you can do. The law is the Ley del Suelo de Canarias and is a superior law to anything the local ayuntamiento says you can or can't do. You can read it here http://www.gobiernodecanarias.org/libroazul/pdf/75053.pdf
However, despite being a superior law in parts it does refer to the local laws. So you also need to acquaint yourself with the planeamiento general for your area, which says what you can and can't do on specific classifications of land in your region.
You seem to know your catastral classiffication as you already said the primary use is agriculture but it;s wrth looking up on the plan catastral what type of Rustic land it is, it may be protected for nature or for some kind of economic use that differs from what is on the catastral documentation.
Go to http://visor.grafcan.es/visorweb/
to see all sorts of information on your plot including GPS coords of its boundaries, what the exact land classification is, what the geology is, what vegetation is there now, what crops were grown etc etc.
An architect or aparejador are the only qualified people who can tell you what you can or can't do on your plot. I strongly addvise you to consult with one who regularly deals with your particular ayuntamiento, although in theory you can use someone from anywhere in Spain. The personal relationship between these guys and the staff at the town hall can be helfull hence my recommendation for using someone local. Good luck and post some photos!