If you get planning permission before transfer to the GD it will raise the value of the property and thus the inheritance tax, plus will have long expired by the time the Grandchild is interesting building a house or selling on.
It does not affect the first time buyer status.
Edit: Inheriting is not buying!
You need to crunch the numbers, I would lean towards giving the land directly to the Grandchild. CGT at 20% (for excess of €49,682) is quite low at the moment and I could only see the (%) going up when times get hard. Also hopefully, the properity crash will have long passed by the time she does inherit the land, which will reduce its value and thus tax, if any. Unless my memory is failing me, another point to remember is the 'Thresholds' are eaten into by previous inheritances. So inheritance €50k from Granddad will reduce the Son/Daughter Threshold by the same. This is the form from Revenue for calculating Inheritance Tax: [broken link removed]
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Towger.