Assuming it's for you to build a house for you to live in as your only or main residence.
Capital Gains Tax exempt for your parents. However, there's a clawback if you don't build a house, or if you sell it within a certain time period. It's you that is liable for the clawback if it arises (see link below).
You'll need a solicitor to do conveyancing. Shop around, you'll need a solicitor also if you need a mortgage to build, so factor it all in when asking around. I don't think parents would have to get their own solicitor as it isn't a house, but would need to sign a confirmation that they received independent legal advice. Your solicitor will confirm, as the rules might have changed on this.
Assuming site isn't already on it's own folio, you will need an engineer / architect to draw a boundary map for land registry, but that's straight forward - get whoever is doing your planning applications to do it, the same maps should do, and you'll keep costs down. There'll be land registry fees, but your solicitor will have details, and should include as 3rd party costs when you ask for a quote. It's a while since I saw one, but I think the conveyancing costs were around 750 from memory.
As there's no house, you'll pay 7.5% stamp duty on the market value. But you can claim a rebate of 2/3 once the house is built. You will need a valuer to do a valuation for stamp duty purposes. Depending on where you live, I think this would cost about 150 euro.
Re CGT relief:
This page outlines Captial Gains Tax Relief on the transfer of a site from a parent to a child
www.revenue.ie