The L permit allows a person to stay in Switzerland between 4 and 12 months. He should have a contract from an employer in Switzerland or an inscription to a school (in the Canton de Vaud, he wil in this case have to fill up a form : see
www.vd.ch/fr/themes/vie-privee/etrangers/entree-et-sejour/

If you serach by google indicating: entreprise générale + vaud, you will find the addresses of many enterprises of construction.