3D-Printed Reusable Children's Bingo Board

I need help with designing a reusable 3D-printed board that holds a laminated 8.5 x 11 inch bingo sheet, with a built-in sliding cover system so children can mark each square during play.

Size & Fit:
Must fit a standard 8.5” x 11” laminated sheet
Allow tolerance for lamination thickness
Inner slot: approx 8.75” x 11.25”
Slot thickness: 0.2”–0.25”
Grid Layout:
4 x 4 grid (16 spaces)
The printed bingo card will be on the inserted sheet
The board should align clearly with the 16 squares

Built-in Marking System (VERY IMPORTANT):
Each square must have one built-in sliding cover
Covers should move easily but stay securely in place
No removable parts, tokens, or magnets
Sliders must be fully enclosed within tracks so they cannot be removed

Durability Requirements (CRITICAL):
Please design this to be very strong and resistant to breaking:

Use thick, sturdy components:
Frame: approx 4–6 mm thick
Base: approx 3–4 mm thick
Sliders: approx 3 mm thick
Sliders should be large and simple, not small or delicate
Use enclosed rail/track system so sliders cannot pop out
Include end stops so sliders cannot be pushed out of the track
Avoid thin clips, hinges, or fragile parts
Rounded edges and corners for safety and durability

Safety:
No small detachable pieces
Smooth, rounded edges
Safe for young children
Designed for repeated classroom/therapy use
Material Recommendation:

Please design this so it can be printed in PETG for better strength and slight flexibility (less likely to snap than PLA).

Design Goal:
Very durable (can withstand dropping, pushing, and frequent use)
Simple and clean design
Easy for children to use
Easy to reset between sessions

Deliverables:
STL file for the board
STL files for any built-in slider components (must not be removable once assembled)
Brief explanation of how the sliding mechanism works
(Optional) Render images for visualization

Please include:
Examples of similar designs you’ve created (if available)
Estimated timeline
Total cost including revisions

Thank you!