In the context of project management, using a main contractor is attractive for a number of good reasons. They remove the burden and risk of project managing the build yourself and you have one point of contact to go to for any problems that might arise. You do however have less control over the project and if the builder goes bust, things can get messy. Builders are very efficient but they are mostly focused on speed; it’s up to you to double check this doesn’t impact on quality.