I do construction and can't find where to put the building supplies deduction. ie. Lumber, drywall, roofing, etc.

[VolvoGirl]

Enter materials under Supplies.  Can't you find it?

How to enter self employment expenses

https://ttlc.intuit.com/community/entering-importing/help/where-do-i-enter-my-self-employment-busine...

this is where it was last year, don't know if it changed.

Go to Federal on left

Income & Expenses

Then scroll way down to Business Items

Then click EDIT by the business name and the next screen should be a list of  topics,

Business Profile, Income, Inventory/Cost of Goods Sold, Expenses, Assets, and Final Details last.

Under Business Expenses, Click Start or Update by Other common business expenses

I have to go or I would make you a screen shot.  Maybe later if I remember.

[Hal_Al]

You may use the supplies category. 

Alternatively, you can enter it as other expenses. There, you can label it, for example, as "materials for Jones job".

Do not use the inventory category.