$fn=64;

// --- Parameters ---
width = 50;                // Outer width of the roof
depth = 50;                // Outer depth of the roof
roof_thickness = 2;        // Thickness of the flat roof base
parapet_height = 3.5;      // Height of the top border walls
parapet_thickness = 2;     // Thickness of the top border walls
wall_thickness = 2;        // Thickness of the building walls below
tolerance = 0.4;           // Clearance gap for a drop-in fit
insert_height = 3;         // Height of the bottom alignment lip
insert_thickness = 1.5;    // Thickness of the bottom alignment lip

// --- Calculated Variables ---
insert_w = width - (wall_thickness * 2) - tolerance;
insert_d = depth - (wall_thickness * 2) - tolerance;

// --- Geometry ---
union() {
    // Main flat roof slab
    translate([0, 0, roof_thickness / 2])
        cube([width, depth, roof_thickness], center=true);

    // Top parapet (border wall)
    translate([0, 0, roof_thickness + parapet_height / 2 - 0.01])
        difference() {
            cube([width, depth, parapet_height + 0.02], center=true);
            cube([width - parapet_thickness * 2, depth - parapet_thickness * 2, parapet_height + 0.1], center=true);
        }

    // Bottom alignment lip (fits inside the walls of the building)
    translate([0, 0, -insert_height / 2 + 0.01])
        difference() {
            cube([insert_w, insert_d, insert_height + 0.02], center=true);
            cube([insert_w - insert_thickness * 2, insert_d - insert_thickness * 2, insert_height + 0.1], center=true);
        }
        
    // Simple roof access hatch for detail
    translate([width / 4, depth / 4, roof_thickness + 0.5 - 0.01])
        cube([8, 8, 1], center=true);
}