5 years ago I read this long saga of buffy being turned by spike at 15. I know they lived in the mansion and drusilla was in the fic and it had many chapters and parts. It goes over the course of years and it had its own decorated page on the website it was posted on. At one point spike has black hair. Sorry for the vague description but thats all i can remember but it was amazing

Was it finished? If not, the first one I can think of off the top of my head is Kantayra's Crimson Codex. It had three books completed, spanning many years. She started the fourth but left the "Buffy" fandom before finishing it. However, she posted on her LJ how the story was going to end.

Via the wayback machine: http://web.archive.org/web/20070509010737/www.angelfire.com/me4/kantayra/crimsoncodex/ccindex.html

Here is the link (summary of book 4 + 5 and the epilogue):
http://kantayra.livejournal.com/283179.html