Do you need an Engineer?
Some building jurisdictions require the plan to be stamped by an architect or structural engineer.
Many houses these days are large and complex and the building codes are also becoming more complex. In years past, there was not a lot of engineering that went into most wood frame structures. They were built using rules of thumb and local practices.
Neither architects or residential designers are engineers. Both (and in fact any person) may design what is called prescriptive design. This is what is considered to be pre-engineered and is laid out in the International Building and Residential Codes and generally specifies things like the size of the wood members needed to span a room ceiling or window header spans and sizes or wall bracing requirements for example.
This does not mean that it is simple or that anyone can actually follow those codes. It also does not mean that everyone is as qualified as an architect to design prescriptive elements. Architects most likely at least have one class on basic engineering. (of coarse that could have been twenty years ago and they may not have been using it much since then) Architects do not get tested annually to determine if their beam design skills are up to date but they are tested on basic structural design in order to acquire their license. Residential designers are much less likely to have taken classes on engineering and there abilities where most likely never tested.
In Texas builders and frame carpenters are not required to take any courses on light wood framing systems design. Frame Carpenters, who work on large structures where they are exposed to building inspectors tend to learn the requirements needed to pass a framing inspection even though they may not have a good understanding of the underlying engineering principles. Many builders simply rely on the frame carpenters to know how to frame houses.
City framing inspectors are also most likely not structural engineers. Though these days they will likely have specialized and ongoing training. In Texas, once you get outside of the city limits in most areas, there are no building inspectors. It is certainly possible to find a frame carpenter who has never been exposed to current framing requirements.
The absolute best way to insure that your house is framed correctly is to hire a structural engineer and in particular one who has a lot of experience in wood framing (also foundation design). They are trained specifically to understand complex loads and do that just about every day they are at work. If there is a question as to what size and type of beam it will take to safely span a living room and carry any loads from roofs ceilings or second floors. Then an engineer is the most qualified person to answer that question.
As a house gets smaller and simpler this becomes less critical. Manufacturers who produce structural components such as beams and trusses often have on staff engineers or technicians to determine the proper sizing and specifications of their own components. But they generally do not come out to the job site and make sure that it was installed correctly.
Particularly outside of the city limits and where there is no framing inspector, I recommend that a structural engineer also inspect the framing just before insulation is installed.
There are people who specialize in (private sector) home inspections but I find them to be of highly variable quality. They may be good at general inspections but no one generally has better training than a structural engineer.
If you are not going to hire an engineer than at least find a builder and frame carpenter who have taken classes on wood frame design and or at least have books on the subject (in other words appear to have made some extra effort to educate themselves) The frame carpenter should have extensive experience in houses with similar complexity and which needed to pass framing inspections. Engineers are always available and so the most important thing is that your builder, designer or architect know enough to know when to hire one.
Signs of complexity:
large spans -meaning large open floor areas where there are no walls to support roof loads (more than 20ft.)
Tall areas -walls higher than 10ft.
Second floor walls that do not line up with first floor walls (particularly ones that are in the middle of large open areas below)
Balconies and cantilevers or other structures which may be superficially attached
Beams (structural members used to support floor and roof loads)
Carports and other roof sections without walls to provide bracing. Or where there are so many windows that make it hard to provide adequate bracing.
Houses located in hazardous areas like high wind and earthquake zones.