Identify the equipment before designing the cover
A boiler, consumer unit, gas meter and water stop tap all have different access, ventilation and clearance needs. Start with the exact product instructions and the requirements of the relevant competent professional.
Design for the person who must service it
A cover should open far enough to inspect, isolate, repair and replace the equipment. Removable panels, full-opening doors and clear service zones are more important than making every seam disappear.
Keep labels and controls available
Do not hide warning labels, isolation controls, meters or fault indicators in a way that delays access. If the enclosure changes airflow, heat or combustion conditions, stop and get professional advice.
Treat the joinery as cosmetic only
The enclosure can improve the room, but it does not make the underlying installation safer or compliant. Gas and electrical changes belong with appropriately registered or competent professionals.