How do I create, dry or roast my own barley malt for beer?

You need to soak the grain for 2-3 days first. Just put it in some kind of tub of cold (!) water, and change the water once or twice a day to provide oxygen.

Once that's done, lay the wet grains out in a layer 5-10cm deep in room temperature. Now it will sprout: rootlets and the shoot will start coming out. It will also start heating up. Turn it a couple of times a day to make the sprouting even, and to prevent the rootlets from turning the whole thing into a massive cake of tangled grain. Touch it to make sure it's not getting too hot. If it does, douse with cold water, or turn the temperature in the room down. Let it grow until the shoot (not the rootlets) is about half the length of the grain. This will probably take about a week, depending on temperature.

Finally, you need to dry it. You can do this in a hot air oven (beware of going too hot, above 80C) if you don't have very much grain. Another solution is to make a wooden frame with a fly netting bottom and a hot air fan. Or you can dry on the floor of a heated room. Or even in the sun (watch out for birds and mice). All you really need here is to get the water out by any means possible, to dry fast enough to prevent mould (if you get mould, throw everything away!), and to not go so hot you kill the enzymes.

Expect to get a lot of character and flavour, but lower efficiency than from commercial malts. Mastering malting is a lifetime project, but unless you fail to sprout or burn the enzymes out you will get beer.