1) Obtain fifty kilograms of highly enriched uranium pellets (>90% pure U-235) and store them each seperately. (Iran has been enriching uranium for a while now, but not to weapons production levels. It's facilities are experimental and easily used to produce civilian reactor fuel.)

2) Construct two hemispheres of steel, together large enough to contain all of the HEU pellets once melted. Line the inside of the hemispheres with cobalt-60, this serves as a neutron reflector that greatly increases your yield.

3) Remove two KG's of HEU from the supply and split the rest in half. Melt the halves down and pour them into the hemispheres, making sure to leave a cylindrical indent in the exact same size and shape of the HEU removed and melted into a cylinder shape.

4) Weld the two hemispheres together, but do NOT let the cobalt catch fire. This would be disastrous and something along the lines of chernobyl. Make sure the two halves of the sylindrical indent line up perfectly. And I mean perfectly. Don't try it, but make sure that the cylinder of HEU removed will fit into the socket like it was never removed. For now, fill that indent with lead of the exact same shape as the HEU cylinder.

5) Construct a good frame around the sphere, and make a decent frame going up from the hole in the sphere. At least five steel I-beams in a circle around the hole will do. Create a steel tube of any width, just make sure the actual path through lines up with the hole in the sphere exactly.

6) Remove the lead plug in the sphere and weld the tube on, attatching it firmly to each of your I-beams which should be arranged so that the flat tops are facing inward.

7)Take the cylinder of HEU and make a disc of glass exactly as wide as the total tube, but make an indent halfway into the disc of glass exactly in the center and exactly as wide as the HEU cylinder. Place the HEU cylinder inside the indent.

8) Make a cylinder as wide as you want, but the inside exactly wide enough to fit over the glass and tube, with the end of it being only wide enough to fit around the HEU cylinder. Make it long enough for the area wide enough to fit over the glass being double the thickness of this layer. Weld the bottom to the tube.

9) Obtain a high explosive, such as cordite that will not trigger accidentally during storage or construction, yet will easily force the HEU cylinder through the glass plate and propel it down the tube.

10) Find the distance between the edge of the HEU cylinder and the edge of your glass cap. Mold a block of solid high explosive to be exactly this thick, but exactly wide enough to fit as a cap over the HEU cylinder. Place the cap on.

You now have a workable nuclear weapon. Conduct the next steps with EXTREME caution in a clean, static-free environment. Trigger that explosive and you have a mushroom cloud.

11) Create an aluminum cap wide enough to fit over the entire top of the tube, wide enough to fit over the glass cap and the explosive. Drill a hole through the top wide enough to place the detonation trigger for the explosive, but do not wire it yet. Place the cap over, weld along the bottom of the joint between the glass's cap and the new cap.

12) Grab an altimeter and find a way to electronically send an electric pulse once a certain altitude is reached. Wire the output of this to the detonation trigger, but do NOT touch the altimeter beyond that, simply fasten it to the top of the cap.

13) Plate over the frame all along to the altimeter, but keep the tip of this cap on the back outside of the plating. Make it aerodynamically sound, make sure to keep everything even, and put tailfins on the back to keep it falling straight.

You now have a nuclear weapon that is ready to be armed in the air, and dropped on some unsuspecting enemy city.