Attic expansion without insulation (insulated intermediate ceiling)

Hello, I purchased my house (built in 2008, low energy, 26 cm external insulation, triple glazing, air heat pump with room ventilation, solar thermal) in 2013. The house has 2 floors + attic. The ceiling between the top floor and attic is insulated. Insulating the attic is not sensible for building physics reasons (no room ventilation). However, I use the attic as a storage space. I would like to make it look a bit nicer. Currently, I look directly at the underlay membrane, which is overlapped but not glued. As a result, hundreds of flies gather in spring and autumn, crawling through the overlapping underlay membrane. I would like to glue the joints with special tape and then (for aesthetic reasons) cover the roof truss with OSB boards, which I want to equip with ventilation grilles. Is it advisable to glue the underlay membrane, and might I create a moisture habitat by doing so? Does anyone have experience with attic conversion without insulation (insulated ceiling between floors)?