How to patch and then repair this broken drain cover?

http://www.dicegeorge.com./psb/psimg...0418-0407s.jpg

It had a 24inchx16inch metal drain cover
over a 2footx4foot hole
balanced on bits of stone.

Eventually I'd like to be able to park a car on it,
for now I don't want kids falling in it!

How are drain covers done nowadays?

[g]