Is their a Time Limit on how long a job can run. I have 1 at 10 years and not C.O.ed, Another at 6 years, This one he hired labors to do Plumbing, Tile, Framing, he purchased laser levels for them and floor was over 2" high at one end. Then they had to rip up the
24" Marble Tiles and start over. Countless screwups. The cost of wire incresed dramatically over the 6 years.
What is good to put in a contract concerning a Time Limit?

I think I would put an economy clause in it stating that if the prices go up due to the economy the parts estimate can go up accordingly.
The marble tile sounds like the fault of the contractors so they would have to eat that. Not the people who hired you's fault.

I love jobs that neverend, change order after change order.

What I think you need to incorporate into your contract, if no provisions for higher costs for materials are included, is to consider a FORCE MAJEURE CLAUSE.

See, for example:
http://www.porterhedges.com/PublicDocs/ArticlesandNews/ForceMajeureNestel.pdf

Getting Adjustments When Material Prices Increase Requires Planning (http://www.midwestconstructionlaw.com/Articles/getting-adjustments.htm)

Do a websearch for "force majeure clause on material costs", and do your research.

May need to get your attorney involved.