[Closed] Planning question, self build in Snowdonia National Park.

Hello, first post so go easy, i'm interested in a building plot in Wales to build a bungalow and eventually retire there to ride trails till my legs drop off, have seen a plot for sale with detailed planning for a 4 bed house and foundations are in, does anyone know if i applied to change plans to 2 bed bungalow would this be looked on favorably, i've phoned the SNP planning dept but the person i spoke to was a bit vague to say the least.
I live in the West Midlands.
Thanks in advance for your gems of wisdom.