This is a big question that seems to have no correct answer. The answer to this question is based on individual builders. Just because you're getting a good buy on the home does not mean that you're getting a good buy on the floor covering. Normally the standard floor covering is garbage. Carpeting is cheap and padding is a thin as single ply toilet paper.
Tiles are generally smaller in size than optimal.
Keep in mind that this may vary from builder to builder so make sure you know exactly what you're getting. Allowances or credits for getting your own flooring will also vary from builder to builder. Generally you have 2 options with flooring. The builder will probably offer several upgraded high quality flooring packages but you will pay more through the builder than you would pay if you bought the same quality flooring on your own later. The other option is to let the builder put in the standard package and have it replaced after closing.