Quite a bit different from the subfloor and wall framing, the loft requires a bit more work. In these plans the 4×4’s are notched out half their width and ideally fit together tightly based on how precise your measurements and execution is. At first I noticed several notches needed to be shaved down. I feel this has been a good result so far since it is better to have cut less than more and still can work to get the beams fitting tightly.
To create the notches I penciled in the depths and widths of the needed cut as then carefully circular sawed to the edges and between the lines with my blade at the depth needed. Then with the space out in a linear fashion, the left overs can be chiseled down to the surface of the blade marks. Ideally the depth of the blade marks will be the smooth surface needed to create.
Here are some photos showing the process and progress: