Well first its a speech so dont forget to write your greetings to the audience.
Next you should start on suggesting on how to make your school beautiful. plan on doing a clean-up activity. You should include teachers, staff and all of the students to make it a bigger activity and will take a shoŕter time to complete the cleaning.
You should also suggest to have a mural session to enhance the schools quality. This way other people who visits the school can be in awe on how lovely your school is.
Lastly say about your conclusion of your speech and say thank you.
Remember to write well and avoid grammatical errors. use bombastic vocabulary. Hope this helps.