Before jumping right into creating a roadmap, it is importing to define what problems to solve, who are the customers/users and what high level use cases we are trying to address. If this is a domain-specific problem, then narrow it and apply your knowledge); if no domain it is still important to highlight the importance of understanding customer and job-to-be-done.
A roadmap comprises of Objectives and Key Results. To arrive at a set of objectives, one needs to be able to classify the requirements into 3 buckets:
1) business – does the objective generate result that affect such metrics as revenue, churn rate etc. ?
2) customer – does the requirement directly come from customer themselves ?
3) product – does the requirement align with product vision ?
The next step is to assign effort in each item so that one can figure out ROI. Attempt to come up with a roadmap that maintains a balance in each of the 3 buckets at any given chunk of execution time frame (3 months if you do quarterly planning). However the key of creating a roadmap is communication – ensuring all stakeholders are aligned or at least understand where you as a product manager came up with the roadmap that you did.