I have 3 little movies of the pair of Longtailed Tits building their nest, taken over 10 days. I will post all three today. Here is the female having built the first 3rd of the nest. It looks like a conventionally shaped bird's nest so far but note the tilted level of the top. This angulation will continue until the hollow is a hole, right over to the top side and a 3rd of the diameter that it is now.