Header for LPG cylinders

What you're looking for is a manifold system.You can make one using a combination of high pressure hoses, ball type gas valves, various pipe fittings and aluminum or copper pipe/tubing. Or you could have a manifold block made for you from solid aluminum then add the hoses/tubing, etc...

It's not particularly hard to do but could get confusing if you're not sure how to configure all of your components.

Best bet is to have a professional plumber set it up for you (if one is available). It's worth the cost given that you are working with flammable gas.

Well, I agree a profesisonal to assemble a manifold to you would not be so expensive compared to the risk. And what you want to do is not that complicated or expensive at all. But, if you insist in doing it yourself, be sure to buy all connections and hardware rated for gas use. Here in my place you can buy all that stuff in the places they sell the hoses, clamps and valves for gas, they are all standard-sized, so, I'd have no chance to change its size either. They also have certifyied hoses that should be replaced in a 5-year basis. You could only buy a set of pressure regulator and shutoff valve, "T's" for connecting all the stuff, and proper hoses to join it all. That simple. But, of course, I know nothing about your local regulations for this kind of installation. And this answer is not applicable if you have a long distance to go from your cylinders to your stove.

In the UK, get a registered professional to set all this up, and make sure an inspection report is available. Send a copy of it to the building's insurers.