rent allowance and mortgage interest relief

I am a PAYE worker currently renting a room in a house for which I claim rent relief (approx 250 euro a year). I only reside in the house during the week. I am currently building a house that I intend to use at weekends only. I am a first time buyer (builder in this case).
I am wondering if I can claim rent relief on the room I am renting and claim mortgage interest relief on the house that I am building that I will be using at weekends.
If I cannot claim both which would be best to claim in financial terms? - the rent relief or the Mortgage interest relief. The mortgage I have is 140K

Any ideas?

No you cant claim both, your mortgage tax relief will be approx. €67 per month €805 per year. So more financially beneficial to claim mortgage tax relief.

Thanks for clearing that up.