Depreciation and tax deduction questions

[Margaret Jay]

Some questions for investment property: 

1) when you buy a house, does the 'clock' on the 27.5 years start over, regardless of when the previous owners bought it?

2) what is a ballpark building vs. land ratio to use when trying to trip out the building value on the overall purchase price (example: if buying a $100k property, what % is typically building vs. land)

3) Can you include improvements/enhancements made onto the building value in depreciation?

Thank you in advance