Help your child to flatten the cereal box and cut off the flaps on the top and bottom of the box.
Remove the front panel of the box. What remains should still stand on its own.
Flip the box so the flat cardboard is facing up.
Have her cut down the skinny sides of the box so they are half as tall as the center panel.
Then, ask her to trim the top of the center panel into a roof. She can create any type of roof she likes. If your want you can show her some examples including a slope, angular, or even a flat roof.
Ask her where she wants the doors and windows. She can use a ruler to help draw them in so they're straight.
Help her to use the scissors to cut open the door on the right vertical side and along the top.
Help her use a craft knife to cut open the windows. The shape that will be cut is a capital "I." This will allow her to fold back the flaps to create shuttered windows.
Now, she can decorate her house with markers, decorative paper or even paint.
When she's finished, have her fold out the box so it can stand on its own. If she likes, she can add scenes by drawing them on white paper and taping them behind the windows and in the door. She can also draw and cut out flowers for the windows.