Mon bureau est au premier étage.

French bureau can mean:

• the piece of furniture (a desk),
• a room where you work (an office or study),
• an administrative office (e.g., le bureau des admissions).

In most workplace contexts, Mon bureau est au premier étage will be understood as My office is on the first floor (i.e., the office room). If you specifically mean the piece of furniture, context usually makes that clear; to be extra explicit you could say something like Mon bureau (le meuble) est au premier étage or specify the room: Mon bureau (le meuble) est dans ma chambre au premier étage.

Not always.

• In French (and British English): le rez-de-chaussée = ground floor; le premier étage = the floor above the ground floor (British English: first floor).
• In American English: le premier étage corresponds to the second floor. You may also see building signs using RDC, R, or 0 for ground level.

Possessive adjectives agree with the noun possessed, not the owner. Bureau is masculine singular, so it’s mon bureau. Examples:

• mon bureau (my desk/office, masc. sg.)
• ma chaise (my chair, fem. sg.)
• mes dossiers (my files, plural)

Yes:

• Mon bureau se trouve au premier étage (neutral, common).
• Mon bureau est situé au premier étage (a bit more formal). On signs you’ll often see au 1er étage or simply 1er étage.

Approximate: mon byoo-ROH eh-TOH pruh-myé ay-TAHZH.

• There’s a liaison in est au: you pronounce the t (eh-TOH).
• Key sounds: u in bureau is the French u (like German ü), au sounds like oh, -tage ends with the zh sound.

Use the ordinal abbreviation:

• Masculine: 1er étage (so: au 1er étage)
• Feminine: 1re (e.g., la 1re fois) Other ordinals: 2e, 3e, 4e, etc. You may also see 2ème/3ème, but 2e/3e is the recommended modern style. For floors, both deuxième étage and second étage are used; deuxième is more common.