word order - comparative adjective + a + noun

a) When can I use "comparative adjective + a + noun" and when not? When can I add "a + noun" after "comparative adjective" and when not?

b) What is the difference between "comparative adjective + a + noun" and "comparative adjective + noun"?

forum.wordreference.com:

1. It may be a bit longer a wait.

2. Theirs is no bigger a house than ours.

3. How much longer a journey was it to your old job?

4. I would have preferred more modern a style.

Thanks!