That's friggin huge dude. It's a common mistake for myself as well: I tend to do things far larger due to the mental note of the HK's being larger. However one thing to remember is that they're not actually LARGER but rather TALLER. In fact they're only about two times the hight of RTP. AS a general rule of thumb I personally keep external walls at 4 tiles high for regular houses. (unless it has a stone base that lifts it) And five or maybe six for castles. If its a two story building I add one row of tiles over the first four, then another four for the second story. I'd also lower that roof to three tiles high. You're gonna give yourself a stroke if you don't ^_^;
Lastly, I agree with Prexus. Google images is a GREAT resource for chip ref. Besides you're making custom graphics man, why revisit the rtp? .
All in all I wish you luck in your endeavor, and I shall keep an eye out for this topic to help you out in the future should you need it.
