$fn=64;

// Parameters
rows = 4;               // Number of rows
cols = 6;               // Number of columns
hole_diameter = 16;     // Diameter of the marker holes (16mm fits most standard markers)
wall_thickness = 2;     // Thickness of walls between holes and outer edge
base_thickness = 2;     // Thickness of the bottom base
height = 60;            // Total height of the organizer

// Derived dimensions
pitch = hole_diameter + wall_thickness;
total_width = cols * pitch + wall_thickness;
total_depth = rows * pitch + wall_thickness;

difference() {
    // Main body
    cube([total_width, total_depth, height]);
    
    // Marker holes
    for (r = [0 : rows - 1]) {
        for (c = [0 : cols - 1]) {
            translate([
                wall_thickness + hole_diameter/2 + c * pitch,
                wall_thickness + hole_diameter/2 + r * pitch,
                base_thickness
            ])
            // Add 1 to height to ensure clean cut through the top without Z-fighting
            cylinder(h = height + 1, d = hole_diameter);
        }
    }
}