Translation:This building is at an intersection.
Often but not exactly. A 'crossroad' usually refers to a four way junction (i.e. where one road crosses another). 'Intersection' (or junction in British English) can refer to any configuration where one or more roads meet another. So all crossroads are intersections, but not the other way around.
If you were saying "There is a building." or "There is an intersection." then you would use が because the focus is on the grammatical subject of the sentence. The new information is "building" or "intersection" so you cannot use the subject of these sentences as the topic yet. Therefore, the subject marking particle, が, is always used in this type of simple sentence that directly describes existence.
But for the example sentence, "As for this building, (it) is at an intersection." the focus is not on the existence of "this building", but rather on the new information being provided about the building "it is at an intersection."
The existence of the building must have already been established, so you can use it as a topic and mark it with は.