Measure the inside of the house walls and write down the dimensions. Make notes of which walls go with which measurements.
Measure furniture dimensions if you are going to draw the objects in the home for the purpose of placement.
Draw the outside dimensions of the house on grid paper. Scale the measurements to the grid by assuming 1 foot is one square on the grid or 1/2 foot is one square. The conversion factor is your choice.
Draw the lines for the inner walls according to the scale. If there are openings for doors, leave a space for the door to the dimensions of the door opening. For windows, draw the line for the wall, but make sash marks on either end of where the window is located to indicate that it's there.
Write the measurements on the grid paper out to the sides of the lines if you want the diagram to be detailed.
Draw out the dimensions of the furniture on separate grid paper. Color them in with colored pencils to match the colors of the furniture. Label each piece so there is no confusion and cut them out with scissors.
Place the furniture piece cutouts in the diagram according to where they currently are in the room. Rearrange them as you see fit to test out other layouts.