Since you don't own the property you cannot make any major repairs or improvements to the property without the owner's consent because if you make repairs and don't pay the contractor(s) then the contractors will file a Mechanics Lien against the property and the owner will be liable to pay the contractors.If you do repairs to the property and you don't own the property the owner can sue you for destroying the property.Should the seller decide he (or she) no longer wants to sell the property because he either wants to keep it, or he can sell it for cash on the market then he will sue you in court for whatever his attorney can come up with and you can get sued just because the contract the seller wrote has some b.s. that makes in not valid.It doesn't matter whether you are right or wrong when  you get sued because when you receive a Sheriff serves you with a lawsuit you now have to make some serious and hard decisions in regards to whether or not you want to pay an attorney $50,000 to $100,000 to settle the lawsuit that often takes up to 5 years to settle in court.How do I know all this?

What is the age of the major mechanicals (water heater, AC units, etc.)5. 

The issue, of course, is that none of these people manage properties so they don't actually think through the mechanics of their laws at all.

Capital goods/improvements like appliances, mechanical, flooring, a roof, siding , driveway, etc will have their own schedules as mentioned, but the building depreciation is straight line and easy.  

In KC that'd be 45-50K(depends on mechanicals)

So we were going to add a sun room off the side of the house, problem was when I was in the basement measuring where to punch the mechanicals through we kept coming up 10' short of the outside foundation at ground level. 

Mechanics' liens are not unique to California. 

I have recently found out through title that there is an invalid mechanics lien against property.. 

The property has all new mechanicals and roof, but was built in 1910 and the air conditioners along the back of the house are actually across the property line on a vacant lot.

I’m a fourth year mechanical engineering student at UC co-oping at Mubea in Florence, KY.