Contrary to popular belief, the regulation of construction in Italy very strict.
Sicily has a history of construction without building permits, but in recent times the state has worked hard to ensure that rules followed. It can sometimes feel over-restrictive, but one should bear in mind that the background is the desire to push for a continuously beautiful Sicily.
This means that you should not take a chance and buy land without being fully aware of what you can and cannot do on it. It is not a very pleasant thing to buy a piece of fine land, and then not be allowed to build in the manner you wanted to.
Basically there are two types of buildable land. The first is ordinary building plots, registred as habitable land. Here it is stated from the outset how large you can build. These plots are not that extremely easy to find. The reason is that there is usually an area with a number of building plots in residential areas, and these are usually utlised by local developers who buy the entire area, build and sell finished homes.
The second type is agricultural land. Basically the rule is that you may build 100 sqm per hectare (10,000 sqm) of agricultural land. But watch out, there are many exceptions. It depends on the distance to the sea, other houses, if it is located in a protected area etc etc. Make sure to carefully check what applies to the land you’ve found!
There are also a host of other anomalies, such as whether it can be shown that in the past there has been a house of a certain size (eg, footprints of old buildings) on the grounds. These can generally be rebuilt.
But as I said, take nothing for granted, always make sure to get a professional investigation as to how much and how you can build on the particular plot. We will of course be happy to help. If you want to resolve it without our assistance, contact a local Geometra to collect documentation on the ground and communicate with the municipality.