I think your project deserves it own thread. There are a bunch of stickies at the top of the list of this forum. All of the parts between an AR15 and its 308 counter part are named the same but most of the parts are different.
What you need to be careful of is that there is not set standard (unlike the ar15). So be careful as you research your parts list and make sure you components are compatible with one another.
Off the top of my head.
DPMS cheapest build type. Can be had for around $1g. Magpul makes cheap mags for this format. Most credible reports I've seen say accuracy potential is about 1 to 1.5 moa with match ammo. 2-3 moa with mil surp.
Armalite ar10. The original AR. Much higher accuracy potential, sub moa potential. Higher price tag, will not take magpul mags. Mags are more expensive harder to find. Noveske 308 and Knights Armaments are based off this format. Will probably set you back about $2 to 2.5g .
There are hybrids like the Mega. I don't have more info but its worth checking out.
And start a thread, list your parts, where you got them and why you chose them. I for one would love to follow it