Custom doors present their own unique challenges. Weather is a major consideration. It is important to choose lumber carefully. Doors are not very forgiving when tight tolerances are used, especially the larger ones.
Arched doors and transoms can be fun if you like bending. I will go into the joys of bending wood at another time. It is not only the transom but the glass and door stop are curved as well and all with different radii. This results in a rather expensive door no matter what it's made of. If cost is an object avoid curves if possible.