I'm making a garden with no grass growing in it. I have paving instead to give space to walk around and see things from further away. You could use gravel, cobbles, decking or chipped bark to make space without grass or lawn.

If you mean "how do I keep grass from growing in flowerbeds" the answer is "weed them". I'm at a loss to know what you could build to keep grass out.

you can put a special fabric down on the ground to help prevent weeds and grass coming through ~ but it still lets the rain through it

go for gravel!

If you are talking about Bermudagrass, the only thing that stops that is a foot deep, seamless, vertical barrier made out of non-rotting material: concrete, stainless steel, or copper. Anything less than a foot deep, and the underground stems (rhizomes) will grow under. After the barrier is in place, you will need to dig up the entire bed to a foot deep, and sort out all of the rhizomes--chemicals leave residues which will make any vegetables you grow there toxic, even if they don't keep them from growing at all. Fortunately, most other kinds of grass are much, much easier to control!

Tugbrethil! The things we are spared in the UK!! Bermudagrass sounds as difficult to control as bamboo (not "Bamboo", who's quite sensitive, I think).

Do you have Japanese Knotweed as well?

No, thank Heaven! We have nutsedge instead. And white horse nettle (Solanum elaeagnifolium), can be a pain--literally!

I'm always glad we don't have poison ivy - it sounds very nasty!