You can't deduct business expenses before you have a functioning business.  If they didn't start business operations until 2020, you can't do any deducting until then.

Research Start Up Expenses for the 2020 return.

Thank you will research that

 While researching, look up what , at all, may be deducted for federal purposes since this business is illegal at the federal level.

Cannabis returns are a unique animal and have many different rules...some tax office's specialize in this niche market.....you may want to consider if this is the right type of client for your office...it will take much more education from you to understand what needs to be done and what can't be done.

Im in CA and its just so common here, I forget that its still illegal for federal purpses!

"purchased a building & is remodeling to comply with the area ordinance."

None of that is deductible. It is part of Basis = improvements.