Dealing with excessive humidity and a lack of airflow is extremely important, especially in the early stages of planning for these issues rather than waiting until you have already been affected by different types of mold. If you would like to use a professional to help with your project, I recommend looking into the work of the professionals at ag-renovations.co.uk . They focus on providing a complete bathroom renovation service, including the design, supply of materials, installation, completing the job, and all necessary testing/standard.