$fn = 64;

// Parametric Dimensions (in mm)
slots = 6;
slot_width = 10;
slot_depth = 25;
spacing = 25;
wall_thickness = 4;
depth = 50;
height = 120;

// Calculated Total Width
width = (slots + 1) * spacing;

union() {
    // Back Wall
    cube([width, wall_thickness, height]);

    // Base Shelf
    cube([width, depth, wall_thickness]);

    // Left Side Wall
    cube([wall_thickness, depth, height]);

    // Right Side Wall
    translate([width - wall_thickness, 0, 0])
        cube([wall_thickness, depth, height]);

    // Top Shelf with Tool Slots
    difference() {
        // Solid Top Shelf
        translate([0, 0, height - wall_thickness])
            cube([width, depth, wall_thickness]);

        // Subtract 6 Slots
        for (i = [1 : slots]) {
            // Position for each slot
            translate([i * spacing, depth - slot_depth, height - wall_thickness - 1]) {
                
                // Rounded inner end of the slot
                cylinder(d=slot_width, h=wall_thickness + 2);
                
                // Straight channel opening to the front
                translate([-slot_width / 2, 0, 0])
                    cube([slot_width, slot_depth + 2, wall_thickness + 2]);
            }
        }
    }
}