Engine Rebuild/Chassis Overhaul

Im just wondering.. at what intervals have you guys been performing chassis and engine work on your cars? im trying to figure out how far i should push a car before performing the work.. especially because my garage is now rapidly expanding with several high dollar items and i dont want to blow too much cash too quickly.

Personally I do 7000 kms before an engine overhaul and 10,000 for chassis.