Tony, I think it all depends on what the cause of the waterlogging is. Do you have any idea why your garden is waterlogged?

i think it is due to clay soil wondering if geting slabs decking will help or if water will lie on top of these

Sounds to me like you need to be putting in drains. If you simply put slabs or decking on top of waterlogged soil then at some point this will get covered in water too.

If your garden soil is so full of clay that it's just waterlogging, you will need to consult an expert. What we do to improve drainage in clay soil for planting is add organic matter and coarse grit. However, if it is really seriously waterlogged, deep down and it's solid clay, then you need to get advice on how to add some proper drainage as moongrower says. Could be a big job and I don't think covering it over is going to be the solution. I live on a new housing estate and have heard some awful stories about this kind of problem on my estate. Thankfully I live in a bit of the former field that isn't too bad and all I've needed to do is a lot of serious digging and adding compost etc. Good luck with that Tony, it sounds horrid!

Check the topography, too. Generally, for drainage, the water has to have a place to go to. If your garden is the lowest spot in the neighborhood, you may have to dig a spot even deeper, and turn it into a pond or "rapid infiltration bed". If the garden is small enough, the latter can be a dry well filled with sand and gravel. If you do that, be careful about the fertilizers and chemicals you use, to avoid contaminating the ground water