Need to create contract for this job?

[Bienes Raices]

The small house I'm buying needs to be repiped. The person who is doing it said it could be done in one day, with a full crew. Do I still need to create a contract for a job that lasts this short a time period? Or would I just pay them the total amount at the end of the day, assuming they finish in one day? (sorry if this is a silly question)