I used a 9" dipole in the old house, Sellotaped to the window. Latter fitted a small aerial on the integral garage roof, but so much depends on where you live, old house I could see Moel-y-parc aerial and my problem was getting just Moel-y-parc, and not Winter Hill.
Here Moel-y-sant is about as good as a chocolate fireguard. So few channels, simply not worth the effort.
In the main we look in local shops, and the lowest gain is 8 db
so even if 4 would do, we still fit a larger than required aerial.
So I have skyQ, loads of channels, and still sit there watching YouTube. Is it really worth it? You can get meters, but mainly to help aim the aerial
the best idea is plugging a TV set in and see if it works.