The cost of a three-bedroom house depends far more on floor area, specification and site conditions than on the number of bedrooms. Two three-bedroom houses can differ widely in price if one is a compact two-storey design on a serviced site and the other is a large single-storey house on a rural site needing its own wastewater treatment system.
Bedroom count is a description of accommodation, not of cost. Contractors and quantity surveyors price from floor area, specification and site conditions. A three-bedroom house might be anywhere from a modest compact plan to a large family home, and the difference in floor area alone can change the budget dramatically.
For a realistic figure, prepare sketch plans first, establish the gross floor area, and then apply a current cost rate or commission a cost plan. If the site is rural, add the cost of a wastewater treatment system, a well or connection works, and any access improvements required by planning conditions.