In most cases, the track is built first simply because of the compactness of the track/supports. It's much easier to build the track first then build a box around the track than it is to build the track within an already built box. (think of it like building a model ship then building the display case around the model ship as opposed to building the display case first then building the model ship within the display case). As others have pointed out, they may simply be building a wall or two of the structure simply because the positioning of surrounding roads/infrastructures would have made building the wall from the other side more difficult. You can already see that the building is going to be quite tall and (generally speaking) taller coasters are going to be more intense. It's highly unlikely that this will be the most intense coaster on property (though most coasters on property are relatively tame by coaster standards), but I'd imagine that it will at least be on the intensity level of Thunder Mountain or Space Mountain.