In my opinion, IA design follows very similar patterns to flowcharting: Add shapes and connect them with lines in an organized fashion to a single document. The challenge when building IA is in understanding how the app or website actually works from the user’s perspective, and how to organize that information into a readable, legible format.
I think there are two major requirements for actually constructing IA: organizing it through a visual hierarchy (that is, a hierarchy of features, functions, and behavior) and creating a legend for displaying different types of features, interactions, and flows. With a standard flowchart, the shapes follow specific requirements (rectangles are processes, diamonds are decision points, etc.)
In other words, the most important factors to building the IA are where individual components of the architecture are placed (hierarchically), and how they’re labeled and displayed.
Organized hierarchy definitely makes the website more accessible.