Deducting detached workshop

You will enter this as an asset for your business.  To do this in TurboTax Online please follow these steps:

1. Within your tax return use the magnifying glass icon to search for Schedule C
2. Click the Jump to link
3. Click Edit for the line of work
4. Scroll down and click Add expenses for this work
5. Scroll to and click Add for Assets - if you don't see it on the list, scroll down to the Less Common section and click the down arrow and show more until you do
6. Click Continue
7. Click Start for Assets
8. You will treat the whole cost of building the workshop as the asset so answer No to Did you buy any items for any business, rental property and/or farm that cost $2,500 or less in 2021?
9. You will also choose No to Did you make improvements to a building you used for this business in 2021?
10. Choose Real Estate Property to Describe the Asset
11. The date purchased will be the date you started using the workshop for your business and then click Continue
12. Choose Nonresidential real estate and Continue
13. Name your asset - Workshop works!- and enter the total cost of buying the base structure and all the purchases to complete the building
14. Leave the land cost blank since this is still your personal property
15. Choose I purchased this asset new and Yes, I've always used this asset 100% for business 
16. Enter the date your business started (which is the date of purchase) and click Continue

TurboTax calculates the depreciation and enters it on your Schedule C for you.

Awesome! Thank you so much. One last question. Do I include finance charges in the total cost of the base structure since I financed it over 5 years? 

The finance charges would be deducted as an annual expense for the business Schedule C as interest.

We have a detached workshop and our accountant is refusing to deduct it on our 2021 tax filing (this is a new accountant to us).  We use the workshop for storage of supplies and actual work.  What article can I point out to this accountant to help convince her that this is a legitimate tax deduction?

Small Business and Self-Employed Tax Center has everything you could ever want including Expenses, Business which of course covers Business Assets. You may want to do your own taxes since you know more than the accountant.

@acleantub