Nooooo, that's not right. Make sure you get an architectural specification telling the builder exactly what to use.
[Link to specifications article by architect removed]
But we've done a couple projects one without the specification and one with. It makes so much difference to have a spec as it dictates the quality of your build. Your builder will always use the cheapest materials otherwise which will kill your project...
But! The only items which were up to the builder in the project we did with the spec were items we couldn't see and did not worry too much about in terms of quality e.g. pipework, underfloor heating system, type of studwork. That way we got cheaper spec and items on things that didn't bother us.