To avoid purchasing Revit Structure, we are using Revit Building to model structure. Currently, I am working on modeling the structure of aloft (a new prototype hotel from Starwood).
Revit Building does have structural modeling capability, but as I model the structure of a fairly simple block & plank building (with some mildly semi-complicated roof structures) I am reminded of something that Paul Aubin said about modeling in Revit (although he was referring to architectural objects).
Paul said (and I'm paraphrasing here) that the initial learning curve for Revit is steep. However, after a short time, a user gets to a point where they want more (usually custom families). At that point, they are halted until they learn how to create families.
The problem with modeling structure in Revit Building is similar in theory; although, it doesn't relate to a lack of objects. I can model beams, columns, footings, etc. However, to model structure in greater detail, I need Revit Structure.
If you look closely at the wood structure (which is the support for the roof of the pool enclosure), you can see that the intersections between the beams of different angles doesn't look quite right; they don't really connect very well. The same thing goes for beams that connect at 90 degrees angles (although it looks somewhat better).
Again, this is not to see that structure cannot be modeled in Revit Building (and I am certainly complaining about the capability of the software to model structure!). In Building, I can create a model that can be used for clash detection, visual scheduling and quantity takeoffs. However, I don't quite get the pretty structural picture that I think I could get with Revit Structure.