About making a lawn in clay soil

I read a few comments how to make lawn, including on a clay or waterlogged soil. I am not a gardener, therefore it is difficult for me to decide what is right and what is wrong.
So, I developed a small plan how to make up my garden. I should first of all poison my garden to kill off weeds and moss, mix 10mm dia sharp gravel with sand to improve drainage, then dig up my garden about 6 inches deep and mix clay soil up with 10mm sharp gravel and sand to improve drainage. Then, after I level soil up, I can seed grass on this mixture.
Is it correct idea? Or it is not that simple?
What weed killers would you recommend and where to buy? Homebase and B&Q sell them for quite a high price. One of my friends was making fires in his garden to kill off roots of weeds, but I don't have that much wood to burn (and I don't want to burn fences :lollol.
Thank you.

 

Well your friend is wasting his time.

Glyphosate is the weedkiller you need.

But are you sure you need to go to all that length to eastablish a lawn. What's there at the moment.