I know the FreeCAD forums are a great place to get answers to questions but sometimes viewing a variety of HowTo’s, “I’m trying to do this but” and “is there a better way to” feeds the brain a bit. The fb FreeCAD group has been a pretty good place to browse.
as an example, someone was having problems trying to create this and said that FreeCAD couldn’t let him put sketches on faces. Lots of people said that wasn’t true and people put sketches on faces in FreeCAD all the time. But you didn’t need to do that anyways…
then there are lots of discussions about how to build it and then this guy says:
I start with a cube and make some cutouts, then I create a new body, copy some edges from cube body, make a sketch and then a pipe: