It seems for purposes of documentation, a builder's log can be as comprehensive or as spare as you like. On two separate occasions, the STL FSDO was satisfied I built the airplanes and issued the Repairman's Certificate even though I presented the local office with (besides the standard forms) nothing more than photo albums and purchasing invoices.
For me, often using a digital camera is an ideal, inexpensive, and instant way to document work and I have accumulated thousands of digital images of anything and everything associated with my airplanes.... before and after construction. The information is organized into easy to access files. For instance, I photographed every detail of fuel tank construction. Once the tanks were closed up for good, it can be difficult, especially years later to recall specific details. After accessing the "Wing" file, I can click on the "Fuel Tank " sub file. Other sub files contained within the "Wing" file contain photos detailing "Ailerons," "Flaps," "Pitot Tube Installation", "Landing Light Details," etc.
Taking photographs has proven to be an ideal way for me to access particular information and I often use the images to share knowledge with other builders.
But storing and retrieving images has other advantages too. Recently, a builder asked how I installed the ELT antenna. Since I had no really good detail photographs of the subject area, I took a new round of photographs to add to the constantly growing collection of images. After downloaded and reviewing the images, I noticed a small nut that helps retain the OAT probe was gone! Who knows how long it was missing? That subtle little detail was apparently overlooked during a routine preflight inspections but thanks to the ease and comfort of reviewing photographic images on the computer monitor, that nut will certainly be replaced before next flight.
Not only did a photographic "builder's log" serve me well during construction but to this day its ever growing collection of photos continue to prove helpful even as I fly machines completed some time ago.