Spanish to English Other Construction / Civil Engineering

This is talking about different types of contracts. This section is on turn-key contracts. Right now I am using plan or design, but I think there may be a better, more speciifc term. It is either accompanying documentation for the contract or an appendix of it, I’m leaning towards the former. TIA!

The original:
Requiere como mínimo de un buen proyecto básico. Éste servirá para la preparación de la oferta “llave en mano”, la cual requiere de mayor tiempo de preparación que una oferta convencional, ya que será necesario desarrollar un “mini-proyecto de detalle” para valorar las diferentes partidas con la mayor precisión posible.

My rough draft:
This type of contract requires at least a good basic plan. This will be helpful in the creation of the turn-key bid, which requires more time to prepare than a conventional bid, since it involves the creation of a detailed mini-plan to assess the different elements with the greatest precision possible.