What proof for market value for CGT purposes of gifting house abroad

We are gifting a house in Greece in an area with limited property transactions. Is market value simply some valuations for estate agents? How many do we need? In terms of costs to offset are garden landscaping and paving etc allowable, refurbishment costs etc and what is required in terms of receipts?

[Display name amended - Admin]

Hi,
You would normally need at least 3 different agents to give a valuation in order to get an average. 
For allowable expenses please refer to: 
CG15180 - Expenditure: enhancement expenditure - HMRC internal manual and
CG15250 - Expenditure: incidental costs of acquisition and disposal - HMRC internal manual
Thank you