The control system is only a part of the solution to regulating temperature. You've not stated much about the whole problem - maybe this is a homework assignment and some assumptions can be made or have to be made.
no sir, its a coffee maker. i will be building a clay pot with embedded heating elements (ac, thats the idea anyway) and i need the water to remain at about 200 degrees farenheight while its on.
You might use an LM35 temperature sensor and connect it to a comparator. The second input of the comparator will determine the setpoint (when to switch on the heater).
Use a transistor at the comparator output to control a relay which in turn controls the heating element.
Think of the elevation of your location. 200deg/F (93.3deg/C) can be done up to 3000ft elevation. Exceeding that the water will be boiling at this temperature and create steam.
180deg/F (82.2deg/C) is normally used to keep coffee "burning hot".
You could modify a soldering iron temperature controller, with the output driving a triac or relay connected to the heating element. Noma brand block heater car cords with digital timers can also be used, simpler and more cost-effective.