How is this different from an administrative assistant resume?

The assistant resume centers a person's calendar and documents. This one centers the workplace: vendors, coverage, and what you could approve. If you did both, give each its own lines.

Should I include a budget?

Only if you owned it and may share it. Otherwise describe the approvals: what you could order and what needed a signature.

Office manager resume tips

An office manager resume should say which workplace you ran and which levers were yours: vendors, the front desk, supplies, visitors, badges, or a move. Supporting one executive's calendar is assistant work. Running the office is the facilities and people coordination. Write the one you did, or both if both were true.

Cover letter for an office manager

What to put first

Name the site: a single suite, a clinic, a studio, or a small company where you were the person vendors called. Then the approvals you had. The first bullets should be recurring work, not a slogan about keeping things running.

Vendors and the space

Name what you bought or scheduled: cleaning, supplies, the copier, repairs, or the landlord requests you chased. If you could spend only inside a limit someone else set, say that.

The desk and the staff

If receptionists or coordinators reported to you, say what that meant: the schedule, the coverage, the visitor standard. If you were the only person at the desk, say that instead of implying a staff.

Onboarding logistics

Badges, keys, equipment, and the first-day setup are office management when you owned them. Do not claim you hired or set pay if human resources did that and you only prepared the seat.

An example line

Adapt this only where it is true for you. It is a shape for a bullet, not a claim that a particular person did this work.

Ran a single-suite office: scheduled cleaning and repairs, kept the front desk covered, and set up badges and equipment for new hires that human resources had already approved.

What to leave off

Leave off an executive calendar you did not keep, hiring authority you did not have, and a lease you did not negotiate. Leave off "wore many hats" in place of the vendors and the desk.

Questions

How is this different from an administrative assistant resume?: The assistant resume centers a person's calendar and documents. This one centers the workplace: vendors, coverage, and what you could approve. If you did both, give each its own lines.
Should I include a budget?: Only if you owned it and may share it. Otherwise describe the approvals: what you could order and what needed a signature.