I recently started my own company, providing operations consulting for small businesses. I don’t have an office, I just use a spare room in an apartment that I rent. Can I claim my rent to be a business expense?

Since you are self-employed, you can claim a certain percentage of your rent as a business-use-of-home expense – so long as you use the room as your principal place of business.

Anyone works from home as an employee, conversely, will need a T2200 form in order to claim rent and other business-use-of-home expenses. T2200 forms are provided by employers.
Get or more information on business-use-of-home expenses