The exterior elevation is much like the foundation layout sheet. While there are dimensions that must be adhered to such as the finished floor and plate height and the roof pitch, there are things that can be changed is absolutely necessary. Things of a more decorative nature can always be changed or altered to better suit your own specific style. Things like banding detail, sill detail, and roof tile (or shingle type) can be changed, but following the plans will assure the best results.
Many times we see our homes built where exterior details are overlooked or given less than the desired attention. This always results in a home that lacks the detail that makes it memorable. It may seem like a reasonable idea to substitute a 8 inch square post with a 12 inch square post, both being structurally suitable. However this will detracts from the overall balance of the design.