"....can I use Section 179 to deduct my" build out" or improvement expenses in a single year?"
That would be dependent upon the type of improvements made and whether or not the business has sufficient taxable income (i.e., there are income limitations to Section 179).
You might want to start by reading the following IRS guidance and, particularly, the embedded link.
https://www.irs.gov/newsroom/irs-issues-guidance-on-section-179-expenses-and-section-168g-depreciati...
Further, you should be aware that Section 168(e)(6) of the Code defines qualified improvement property as "any improvement made by the taxpayer to an interior portion of a building which is nonresidential real property if such improvement is placed in service after the date such building was first placed in service". However, it excludes improvements for which the expenditure is attributable to the enlargement of the building, any elevator or escalator, or the internal structural framework of the building.
