Just a little FYI. The shape builder tool is good but in many cases will add multiple anchor points to the design which in turn will increase your file size. Depending on how complex the shapes you are trying to create. Try making 2 squares one larger than the other and using the shape builder will result in a clean path. Try doing the same with circles (depending on the size of the circle) it will add anchor points in the middle of both centers. So instead of having 4 anchor points you will end up with 8 and if you have a very large circle this can be 16.
If sending this file to a cad device or a vinyl cutter ( Roland or Cricut etc.) can and may leave you with jagged edges, longer print times, or worse an unprintable file.
Using the pathfinder tool also has its limitations as a boolean operator (mathematical algorithm), precision on the intersection is not exact at times and can lead you to an off-centered or off-measure output. Meaning if you are trying to keep the design in a measure of 100 points x 100 points and depending on the shapes your intersecting, your final results could end a little short (99.99 x 100) do this across multiple shapes or paths and the final result could be way off. When creating logos or isometric concepts where you want precision, this will affect your final results.
This is something over time you will know what tool to use and on what shapes to use them.
Sometimes I will use the shape builder tool or pathfinder to just get an outline that I convert to a guide later. Saving an extra copy of the original shapes before using any of the tools so you won't need to recreate the shapes/paths after conversion will help save you time. After the guides are made then I use the scissors and pen tool to limit excess anchor points and guarantee precise alignment and measurements.
It is also useful doing it as mentioned above that you can have total control over the final output by rotating circles so the anchor points align on sections that are being cut and or moving the anchor point out of the path that is going to be used. ( Limiting anchor points in a document ).
Ok so this maybe a little to advanced for many but good info for future projects.