ASCE 7 addresses the general setup conditions, but doesn't dictate how you get there. Many engineers still do hand calcs, so the technique for doing that type of analysis is going to be different than if you are doing a full FEA.
As an example, it is sometimes easier to do a few hand calcs and develop the roof structure reactions, then apply those to an "open box" FEA model. That saves the time and effort to build each truss/joist/dummy beam for the roof into the model. It makes the interpretation of the results easier and also makes it easier to troubleshoot your model if you are working with a notoriously "buggy" FEA program. Depending on the complexity of your model, they can "blow up" on you pretty easily sometimes.
So, IMHO, ASCE 7 sets general parameters from which we are to use engineering judgment in the application of those parameters. They cannot set parameters with such site specific parameters as building geometry, building design parameters and other items that would be specific to your building, but they give you the tools to set those yourself.
In your case, you can do it either way you'd like. You might even want to try it a couple of ways so that you'll know the differences and can look for special cases. If you have built a full FEA model, it's pretty easy to change the load conditions. If you have a partial model, same thing. If you're doing it by hand...simplify!