You can make your own assessment of the cost of rebuilding your home using the cost calculator.  The guidance figures provided are based on specific examples of houses of average quality, built using standard construction methods. However they are not applicable to:
• flats
• properties built of stone or materials other than brick
• properties with more than two storeys or with basements and cellars
• houses with special design features, historic or listed buildings, or houses which are larger than the examples
• houses other than of average quality.
It is stressed that these tables are no substitute for professional advice and judgement, particularly where a property has any unusual features.  You can instruct a member of RICS to prepare a professional Rebuilding Cost Assessment for insurance purposes. 

A Rebuilding Cost Assessment will normally be carried out by taking detailed measurements of the house and using the rebuilding cost information provided by BCIS. However, this may not be appropriate in certain circumstances where the method of Rebuilding Cost Assessment will need to be specially agreed.

The cost calculator can be accessed here.

You can Find a surveyor here.