How can i fit a simple LED light in a small model house?

You'll need a DC voltage source, and the voltage spec's of the LED. Subtract the LED's working voltage from the source voltage, and divide the result by .02, which will give you the value of the resistor that you'll need to drop the LED's input voltage to a level that won't burn out the LED. Find a resistor that has a higher (not lower) value than the amount from your calculation, and wire it in series with the cathode (negative side) of the LED.