The first issue here is whether this building is still a habitable house under planning law. If it isn't, you will need planning permission. Creating a new habitable dwelling almost from scratch isn't part of the Exempted Development Schedule.
The description you gave with only one wall standing suggests this is a ruin. It is unlikely that you will be able to "restore" such a dilapidated structure economically. You will have to clear the site.
This suggests you are paying from €40K up for a site. There may be legal fees, so allow €2K you'll need planning permission for say €2K and on top of that you will have site clearance costs of anywhere up to say €20K or more. €74K so far.
Then you will have to build a new house, and a compliant house in the current economic climate is from €80 a square foot minimum keeping it legal. Your Council levies will be €15K in Dun Laoghaire Rathdown. €89K and you haven't started to build.
Say you build a modest 1,500 sq.ft two storey detached house for €80K a square foot - that's €120K so you're looking at circa €209K without paying any professionals to take it to site or certify the monies.
Feel free to criticize my figures, but you have to tot up realistic figures for a project like this or as other posters have warned, you could end up sinking a lot of money into this project, for almost no return.
By that I mean when you tot up total costs of say €220K and you see what houses in the area are fetching on the open market, you might have no profit on a sale. Plus the Estate Agent will look for 1.0-1.5%!
Think very carefully about this one.
ONQ.
[broken link removed]
All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.