control design of doors,lights and gates interfacing with a pc

Ever hear of SSR's (Solid State Relay's)? They are optically coupled triacs which require very low voltage and current to control AC. You can use your printer port to control them. To test the interface safely you can even use conventional LED's w/ resistors, and replace them with the SSR later.

The printer port may not have enough control lines, you'll have to figure that one out yourself.

http://ourworld.compuserve.com/homepages/Bill_Bowden/page6.htm#PPRIC

BTW, the same printer port can also be used as an input.

SgtWookie had an excellent suggestion concerning this idea though, buy a printer interface card. If you slip and burn it out you don't have to replace a motherboard. They're also pretty cheap too, another bonus.

Does "control" mean open and close remotely, or just monitor the state of each gate and door?

can you help me with the circuit for controlling lights,gates and doors in a building by using a pc as the controler

You can´t read, can you?
If you can, read what beenthere said and think about it.