Learn Hardcore Catalan: En aquest edifici hi ha un ascensor, però jo prefereixo l'escala. - In this building there is an elevator, but I prefer the stairs.

Hi ha is the usual Catalan way to say there is or there are. It comes from the expression haver-hi. The hi does not need a separate English translation here; it is just part of the construction. For example, hi ha un ascensor = there is an elevator, and hi ha dos ascensors = there are two elevators.

Why does the sentence start with En aquest edifici?

En aquest edifici means In this building. Putting this first sets the location before giving the information about what is there. That word order is very natural in Catalan.

Why is it en aquest and not a aquest?

For location, en is the standard and most natural choice before a demonstrative like aquest. A aquest edifici more naturally suggests direction, like to this building. In some varieties there is some overlap between a and en, but en aquest edifici is the safest standard form here.

What does aquest mean, and why is that form used?

Aquest means this. It is masculine singular because edifici is a masculine singular noun. The other forms are aquesta for feminine singular, for masculine plural, and for feminine plural.