Yes, it will have to go on the roof for sure, the attic won't cut it with the tile roofs you have there.
A tripod mount on the roof peak would be best, but it's problematic with a tile roof. I ended up using a chimney mount. Some people say they put a lot of stress on a chimney, but our chimneys are reinforced for earthquakes, so I think an antenna there would be OK. It sounds like using the pole for your (former) dish should be the easiest and will be your best bet.
BTW, you'll be pretty jealous of my TV Fool report I pick up everything crystal clear with a dinky little Channel Master antenna. The only reason I went through the trouble was because I was putting a ham radio antenna on the same mast.
http://www.tvfool.com/?option=com_wr...134984c258d029
Good luck!