DIY- Best Generator Shed with noise isolation. Firman generator or other types

This is a generator shed i've made for taking the noise level down a lot. It is really effective and it cost me around 600$.
Size is : 30"x60"x48"approx. Be sure to choose the right muffler extention for your generator model. Mine is a Firman.
Be aware that the shed should be installed at least from a distance of 20 feet minimum from home or any air inlet.
Muffler: Just look on ebay and search for "muffler extension for generator" There are plenty of model available. The link i've used had changed.
Exhaust system: www.zombiebox.com/shop/honda-...
Exhaust Fan: www.amazon.ca/-/fr/gp/product...
Gas Strut:www.amazon.ca/gp/product/B07K...
Inside insulation with Rockwool Safe'n'Sound from HomeDepot and covered it with fireproof cement board in it.