There are disclosed a plant and a process for building different types of green tyres for vehicle wheels for each tyre size, through the use of elementary semi-finished products, the process comprising:a) building a carcass structure of a green tyre, said carcass structure comprising at least one carcass ply and a pair of annular anchoring structures;b) building a crown structure of a green tyre, said crown structure comprising at least one belt structure and a tread band;wherein at least one between the building of the carcass structure and the building of the crown structure comprises:c) providing at least one first feeding unit of a first elementary semi-finished product and one second feeding unit of a second elementary semi-finished product, said at least one first and one second elementary semi-finished products being different to one another;d) building at least one portion of a structural component of the tyre being processed starting from at least one of said first and second elementary semi-finished products, in one work station fed by said first and second feeding units of said first and second elementary semi-finished products.