The roofline on a house has a big impact on how the house looks. Sometimes the pitch of the roof might be too flat or oddly shaped, and in order to maximise house's potential, or expand attic space into usable square footage, the roofline must be changed. While serious rebuilding such as a roofline change is not insignificant, the cost isn't as much as adding a new floor, and the resulting space can be well worth it.
Take photographs of the house from all sides. This is best done on a ladder to accurately show the roof as much as possible. If the house is more than one story, it might be necessary to take photos from further away or even from a neighbour's upstairs window.
Measure the exterior walls of the house and plot them out on the graph paper at a scale of ¼-inch equals one foot. Tape several pieces of paper together if necessary so the entire house is on one piece.
Overlay the footprint (graph drawing) of the house with tracing paper, taping it down to the graph paper. Draw the existing roofline, recognising that most roofs have a centre ridge line. Use the ruler as necessary to approximate how the roof would look to a person in the air above it and looking down. Check with the photos or go into the attic space if possible and measure or check what you see. Once the existing roof is plotted out, it becomes possible to understand how the main and secondary roofs relate to each other.
Determine the reason for changing the roofline (such as increasing attic space to convert into living space). This will inform how the roofline should change to best accomplish that goal. If the roof is simply too flat or has a shallow pitch, then the existing roof plan can be elevated by increasing the pitch to gain interior height. Dormers can be added to a new roof system to provide additional light. If the existing roof is hipped, then the hips can be removed and the king ridge beam can be extended to the sides of the house to form gables. In this case, windows can be added at the gable ends if the interior headroom is sufficient to create a new level for the house.
Overlay the original roof plan with more tracing paper and redraw the roof to reflect the desired changes. When only the pitch is changed, the roof might not change much at all. When gables or dormers are added, rooflines can change dramatically. Plot your roofline of choice.
Blow up the photographs of the house and make photocopy enlargements. Use these to sketch new side views of the house with the new roof. This may include gables and dormers or other features.
Some roofs are quite complex, and how they work together mechanically might be a challenge to understand. If necessary, have an architect answer complicated questions that are beyond a simple roofline change.