For example for "I want to build a good gym routine":
我想建立一個良好的健身計畫。 Wǒ xiǎng jiànlì yīgè liánghǎo de jiànshēn jìhuà.
Here are some variations of the sentence along with their English translations: 我想制定一套有效的健身計劃。 Wǒ xiǎng zhìdìng yī tào yǒuxiào de jiànshēn jìhuà. I want to create an effective workout plan.
我希望安排一個健康的健身日程。 Wǒ xīwàng ānpái yīgè jiànkāng de jiànshēn rìchéng. I hope to set up a healthy fitness schedule.
ps: I am building an app to make learning chinese easier. Feel free to ping me privately for testing :)