Rainsoundbox - Relax with rain

The rain pitter-pattered on the roof top. "Pitter-patter" means light sounds or beats, and often is used to describe the sound of small animals (like cats) as they gently move about. It has a fairly positive and easy-going connotation, and using "pitter-patter" to describe rain invokes a sense of melody and calm.

Rain Sounds - This continuous, uninterrupted recording is ideal for relaxation. It's a natural white noise sound that, similarly to storm sounds, makes us feel safe inside. This recording is taken from the popular Rain Sounds album

I heard the rain thrumming on the roof.
I heard the rain pelting the window.
I heard the rain battering the roof.
I heard the rain drumming on the window.
Or, if you like the drumming idea and want to get a bit more literary about it, how about:
The rain beat a gentle / violent / solemn tattoo on the roof.

The rain sprinkled on the roof top.
"Sprinkle" means scattering or dispersing. It generally is applied to small objects, like dust or sugar coatings. When describing rain, it generally implies that the rain drops are small and gentle. It can imply a feeling of spreading in a haphazard or unguided way. For this reason, it has a fairly neutral connotation, generally meaning light rain.

The rain showered the roof top.
"Shower" means a lot of water, should evoke the feeling of being in a shower. It creates a sense of a large quantity of water, coming down in large drops. It's not necessarily aggressive or negative, but implies lots and lots of water. A "shower" of water on the roof wouldn't be resolvable in individual drop sounds, but would instead be a steady drone of noise.

The rain pelted the roof top.
"Pelt" means to attack with objects. Here, it should evoke a sense of anger or aggression, as if the water were throwing itself in attack at the roof. "Pelting rain" would be large, fast drops, coming down hard.

The rain battered the roof top.
"Batter" means to beat or attack. Generally, it always evokes a sense of aggression and violence. When used with rain, it often implies a type of windy rain, as the wind and the rain "work together" to attack the building. In the minds eye, you might see shutters banging about and hear the whistling of the wind when you imagine "battering rain".

There are a lot more phrases, but these should get you going. If you are looking for a more specific connotation, I'll see what I can come up with.