The design rules depend on which foundry you are following and it varies from foundry to foundry even if you are targetting 45 nm node. Usually foundry will provide a lef file in which all these design rules will be specified.
Check the targeted model library......On which you would like to ride............
Like gpdk180, gpdk090, gpdk045...........
Or
Foundry Models like UMC library Or TSMC..........
Read their Manuals carefully......