We are planning to buy a home built in 1940 in miami Florida.what are the pros and cons of home built in 1940 and what precaution to be taken,how to get the home inspected for plumbing ,electrical,structure.

I have bought homes built in the 1800's before, and have owned dozens built in the 40's, I am not sure of any special miami issues but local inspectors would

I would inspect it the same as I would any home, very complete and very in detail.

Foundation issues, and esp go and check for building permits for improvements, if they have done work without permits it can lead to legal issues latter. Wiring, are they up to code, what type of wire is used, the breaker box has it been up graded ?
Insulation ?

Agree that it is an absolute "must" to have the home inspected. In addition to the areas that Fr_Chuck entioned, you also want your inspecetor to check the roof and see whether it has been retrofitted with modern "hurricane clips." These are devices that help keep the roof from blowing off in high winds - and were typically not used in residential construction until more recently.