Simple Parametric Rocket (made with OpenSCAD)

rocket.scad

module rocket () {
	$fn = 100;
	rocket_diameter = 5;
	rocket_length = 50;

	rocket_nose_cone_length = 10;

	rocket_num_fins = 3;
	rocket_fin_length = 10;
	rocket_fin_width = 5;

	rocket_engine_diameter = 4;
	rocket_engine_length = 10;

	difference() {
		union() {
			translate([0, 0,  (rocket_length - rocket_nose_cone_length) / 2 + ( rocket_nose_cone_length / 2)]) cylinder(r1 = rocket_diameter / 2, r2 = 0, h = rocket_nose_cone_length, center = true);
			cylinder(r = rocket_diameter / 2,h = (rocket_length - rocket_nose_cone_length), center = true);
		
			for( x = [0:rocket_num_fins]) {
				rotate([0, 0, (360 / rocket_num_fins) * x])
				translate([-((rocket_diameter / 2) + (rocket_fin_width / 2)), 0, -( ((rocket_length - rocket_nose_cone_length) / 2 ) - (rocket_fin_length / 2)) ])
				rotate([90, 180, 0])
				polygon(points = [ 
					[ -(rocket_fin_width /2), -(rocket_fin_length /2)], 
					[-(rocket_fin_width /2), -(rocket_fin_length /2) + rocket_fin_length], 
					[-(rocket_fin_width /2) + rocket_fin_width, -(rocket_fin_length /2) + rocket_fin_length] 
				]);
			}
		}

		union() {
			translate([0, 0, -((rocket_length - rocket_nose_cone_length) / 2 ) + (rocket_engine_length / 2)])
			cylinder(r = rocket_engine_diameter / 2, h = rocket_engine_length, center = true)
			;
		}
	}

}

rocket();

The fins don't show up render. Before the polygon command at line 25, add a linear_extrude(1) before that line. Then the fins will show up in the render