Hiring an architect.

Remembering your architect's birthday.

Realizing, too late, that the builder's "architect" was really a drafter/designer.

Just keeping the theme going!

Details are often overlooked unless you remind your builder. Communication is key to prevent things from being forgotten!

A full set of construction documents at the job site?

A pile of money.

Using a good builder.

Small things that get forgotten:

the difference between the "search" box and the "start a new discussion" box.

Get a structural engineer even if you don't need them for permitting.

And if your soils are problematic, a geotechnical engineer is a sound investment to ensure proper foundation type.

I agree with KH. If you don’t hire someone to observe the construction work then you must do it.

Yes, this is an area where many consumers think they can save money, and just turn everything over to a builder thinking everything will turn out right.