Today event

Today i've a plan to go school (It could be easier to say ' I'm going to school' but if you mean that you usually go to school and it's your daily routine it could be better to say 'Today I go to school'.There are many traffic because of heavy rain . (We use but to link two sentences not really at the begining of a sentence)
Roads are flooded so tommorrow i 'll go. ( We don't usually use 'the' in plural)

I was supposed to go to school today but But there was too much traffic due to the heavy rain and floadrd roads.

I will go to school tomorrow.

Today's event

Today I planned to go to school, but there was heavy traffic because of heavy rain. The roads are floaded. Tomorrow I'll go.

Very well written!

Today event

Today i've a plan to go school .But there are many traffic bcause of heavy rain .The
roads are floaded.Tommorrow i 'll go.

Good job!  My suggestion:

Today's event

Today I planned to go school, but there was a lot of traffic because of heavy rain.  The 
roads were flooded.  Tomorrow I'll go once it dries out.