The best place to find N-scale track plans is from manufacturers that make railroad and train models, such as Kato USA. This company hosts an ample list of N-scale track plans to download and immediately start using.
In addition to manufacturer websites, N-scale track plan databases are available online, producing a plethora of options. Model Railroader features a database search engine that aggregates N-scale track plans from a variety of sources. Most N-scale track plans include a detailed layout of the track, a list of part numbers and a list of the quantities of the necessary pieces to complete the project.