How to depreciate building improvement to home office

We have an exterior home studio (570sq/ft) that wife uses 100% for her self employed business.

We made substantial improvements ($20k) to the building so she could use it for her business.  

We replaced the roof, changed the windows, add new siding. 

 

How can we write this off or depreciate the expense? Please tell me how/where specifically in turbotax we enter these costs.

 

Thanks