The size of a plot does not tell you what can be built on it. It is the commune's plan local d'urbanisme (PLU), the local planning code, that sets the rules: zoning, permitted building footprint, set-backs from boundaries, maximum height, sometimes even the external appearance of buildings.
You also need to look for easements affecting the plot: rights of way, buried services, easements over views. These are obtained from the commune's planning department and appear in the documents provided at the sale. Better to know about them before signing.
The nature of the ground determines the type of foundations, and therefore part of the cost of building. A geotechnical survey tells you about the bearing capacity of the ground and the precautions to take.
It is also prudent to consult the documents on natural risks applying to the plot: depending on the area, particular requirements may apply to the building.
An unserviced plot has to be connected to water, electricity, telecommunications and drainage, whether mains or private. The distance to existing services and the connection constraints should be assessed before buying, as they add to the price of the land.
Access matters just as much: a narrow lane or a steep slope complicates both the building works and daily life.
The shape of the plot, its orientation, its access, its views and neighbouring buildings all influence where the future house sits: which way the living rooms face, cast shadows, overlooking, the position of the garage.
A feasibility study, even a brief one, confirms that the project you have in mind really does fit on the plot you are considering, within the planning rules.
Before a purchase, MCI Construction reviews the project to identify the constraints of the plot and the works it implies: access, earthworks, foundations, connections.
The company works in Narbonne and the Grand Narbonne, the Corbières, the Minervois and along the Aude coast, as far as Béziers. The survey and the quote are free.