This is an NLP problem and I was wondering how I should proceed.
How difficult is the problem? Could I replace the word with synonyms and check that the grammar is
You should start by programming easy structures by yourself, doing something called sentence transformation, then make your system available for free and with the option of adding more combinations or alternative structures which convey a similar meaning to the original sentence but using different parts of speech as well as grammatical structures.
for instance, you could write an original sentence into your system such as,
Then another user of your system will help to rewrite the sentence with a different structure but a similar meaning, rephrasing or using the appropriate parts of speech as your system specifies, the more users sign up to your system or download and use the app, the more options will come out after someone types a sentence and expects another one with a similar meaning to the input sentence you, or anyone had given.
it is easier if people work together collaborating in your project than if you try to create it by your self or write all of the sorts of sentences that can be rephrased.
Other examples;
Good luck with your system, let me know how it goes!