Software written and designed by Builders for Builders Back to JOBCOST Enter the external wall length for lower floor and upper floor and then the floor areas, add an amount for scaffolding and then select from the options for roof type, wall type, windows, doors, trench dig and length of any partition walls of either block or stud. Tap info for a review of your selections and cost breakdown and to add any P.C. items for kitchens, bathrooms and central heating.