@NiceGuy, and with all due respect to comments by @obhorst, one thing to be careful about with tax questions is to frame them “precisely”. The question you are asking is actually (I think):
“The corporation uses a bedroom in the home of a shareholder/director (who is also likely an employee of the corporation) as an administrative office. In addition to this the corporation also has a commercial space. Can the corporation claim a portion of the operating cost of the residence as being for the rental and use of an office?”
The answer to that may well be a very different one from that framed by you where the “Shareholder/Director uses one bedroom…”.
It is the corporation (presumably) that seeks to claim the expense, not the individual. (And to complicate matters…when referring to an individual who is both an employee AND a shareholder or director, it is important to note “which hat” the person is wearing for purposes of the question.) Rules that apply to corps are different than in the personal context, and rules that apply to shareholder/employees MAY be different than an arms-length employee.
One approach to this would be for the individual to rent the “office” to the corporation for an amount, report the rental revenue, deducting offsetting expenses on personal tax, preferably with NIL net income. The corporation deducts the rent paid. A formal rental agreement will help, but is not, in and of itself determinative. It can be annual or month-to-month and preferably written.