Electricity metering is a solved problem, simply put all the office receptacles and lights on a single circuit and use a CT (current transformer) and a 120v submeter [0] to record energy usage. Landlords use these for tenant energy monitoring and billing in commercial real estate.

[0] https://www.leviton.com/en/products/1n120-1d

Honeywell even makes a 25A model under the name Emon Dmon: https://prod-edam.honeywell.com/content/dam/honeywell-edam/h...