Construction costs

My son is a self employed Plant Operator in the construction industry. He is now purchasing his own digger and has built a garage attached to his house for the sole purpose of storing the digger when not in use. He has built the garage himself. Can he claim the cost of materials and plant hire? If he can, would he claim it as a business expense or a Capital Allowance?

Hi
He cannot claim the costs of buiding the garage as this would add value to the house and would only be taken into account for any potential capital gains.
For the purchase of the digger, this would be capital allowances.