I agree with most of the others here but add the following; Before you worry too much about going beyond the SoP make sure you have them down backwards and forwards. Nothing looks worse than falling short of something you are required to do while exceeding things in some other area.

In general, nothing is going to bite you like water penetration and insect infestation. Being lucky enough to own a mid-sized company and be responsible for a bunch of other guys I have fielded quite a few complaint calls over the years. Almost without exception, the problem has something to do with water or bugs.

If you want to exceed the SoP I'd go for bulding envelope issues and decks. Safety stuff is good too, things like electrical, hvac and all the safety railings, etc.

HI going down the 'code road' seems be more comman than it use to be so if you're looking for some good classes or certifications look into the first of the one/two family dwelling certifications. That's what it use to be called anyway. Basically, it's most everything to do with how a house is put together except for the mechanical stuff. I've got a lot of use from those classes over the years.

Good Luck!