First, understand the asset is "NOT" residential rental property, any way you look it it. It's non-residential rental property and therefore gets depreciated over 39 years.
Select the Add an Asset button
Select Intangibles/Other Property and continue.
Select Other Asset Type and continue.
Describe the asset, enter what you paid for it, and the date you started using it for storing your rental business stuff. Then continue.
Select "purchased new" and select "No, I have not always used this item 100% for business". Then select ""I first used this item at least part of the time for business,....." Then enter The date you started using it for the rental stuff or whatever.
On this screen you are also asked for percentage of "TIME" you used this item in this business for the tax year. The question is worded incorrectly for your specific situation. The question should be "what percentage of this asset did you use for business in 2020?" So this is where you will enter your 45% figure, then continue.
Select "31.5 or 39 (Non-residential real estate)" and continue.
Select straight line and continue.
Now you see the summary on this asset and can elect to show the details. Click Continue and you're done.
