I hear you need to rebuild a window frame and sill?....Try some of this new PVC trim board......
Home Despot (Florida) sells (never tried it!)Old name Marleymoulding:
http://www.royalmouldings.com/
Here's the manufacturer for the stuff I use in Orlando.......
http://www.azek.com/productinfo.asp
Now you probably won't find the exact profile you're looking for BUT you can glue this stuff up with PVC Cement...........and cut and machine this like wood.......to build a custom window sill........
It's not structural so you'll still need to reframe with (?the P/T)............
use treated screws and a good silicone to join PVC to wood.........
OH YEAH......It's NOT cheap........sells for about $6.00 board foot..........