Sharing a house purchase in the US

Can anyone advise me on the following: I am helping an elderly relative to purchase a home in the US by giving him half the purchase price as a gift. He has recently sold his own home and wants to move to another area, so has some capital already. The house and other assests (investments) are willed to me. Are there tax implications for me (I am a PAYE earner here in Ireland) or for my relative in the US - gift tax, investment tax, whatever? There are two options as I see it. (1) Have my name put on the deeds as a part-owner or (2) Just give the money to my relative and draw up independent agreement with him.

I would think that if you give it as a gift then you will have to pay tax on the entire value when you inherit it.
This does not make a lot of sense if you have paid for half.

Inheritance tax in Ireland only or is there a tax implications from the US side of things?