re: Home fire sprinkler experiences? Updated OP

You should pay someone. And expect to pay a lot. Sprinkler systems have to be permitted and inspected annually and the permitting requires an approved plan by a licensed contractor and both the design and materials have to meet standards. It's not as simple as running some PVC or PEX in your attic. In fact, you can't use those materials for the lines. Furthermore, you may not even have the water pressure to support it to begin with.