A short vowel u story could be like this. There was a duck. The duck was very much in a hurry. It wanted to go to a bush. In the bush, there were some nuts. The duck loved nuts. So, it waddled quickly towards the bush. When it reached the bush, it started to munch on the nuts happily.
Just pick some words with long vowels. For example, use 'bee', 'tea', 'see'. Then make a simple plot like 'The bee drinks tea and sees a flower'. It's that easy.
A short vowel story could be 'The cat sat on the mat'. Here, the 'a' in 'cat' and'mat' has a short vowel sound. For a long vowel story, consider 'The cake is on the plate'. The 'a' in 'cake' has a long vowel sound.
Once upon a time, there was a bee. It was very busy among the sweet pea plants. The bee saw a deep well. It flew over the well, humming a sweet tune. The 'ee' in bee, pea, and deep represents the long vowel e. And that's a simple short story about it.
There was a men. He had a net. He went to the wet land. He saw a nest with eggs in it. He didn't touch it because he knew it was a home for the little birds. This is a simple short vowel e story.