hey guys first post.

I'm a huge downhill Mountain Biker but my brother just got a Cannondale CAD 105 and I've gotten the road bike bug but I want a single-speed and preferably a coaster brake though a normal brake system would be ok. Since I don't know anything about road bikes I have joined this forum for one main reason. I need your help in finding parts for a custom build. My budget is preferably around $500-$800 though If I need to i'll go up to a max of 1k if for some reason its needed but hopefully I don't. I wouldn't be buying the parts any time soon but I'm starting to look now so I can have the money and then go out and order and build the bike.

I'm just under 6' tall and 140lbs.

Any help would be appreciated!