The type of insulation and roof materials are going to play a big role here. If you have that aluminum backed insulation around your walls, it's going to seriously attenuate signals coming in. Same with roofs with lots of metal flashing.
That being said, if you still want to go for it, do a little homework first. Walking carefully, take your scanner with NO antenna (or just use a paper clip) and see where signals for the area(s) you want to hear come in the clearest. Every attic has a sweet spot or two, but you're going to have to hunt to find it. Use a marker and clearly mark on a beam where you find them. If the signals come in well with no antenna (or a minimalist one), then it's likely when you put your antenna up it should work reasonably well. There will be some loss due to what happens to be in and around the attic, but it will work.
When you mount the antenna, mount it as high as you can get it. Height can make the difference.