I prepare my own grains, all from 2 row base malt, and pearled barley, the cheap stuff from the grociery store - $1.00/lb. I've asked my local Kroger's manager to please stock more cheapo pearled barley, and he asked "why?" - now I have someown else interested in homebrewing.
Anyway, I only been AG'ing for about 2 years, but since then I live too far from the homebrew store, I usually make my own grains.
Equipment Needed: Oven, two half-sheet pans, small cooler (mini mash-able), spatula.
For dark roasted grains, you'll need a pop-corn maker, the kind that blow hot air around, or you can use a hot-air gun, and metal bowl.
To prepare your grains:
Roasted Malts: Use them as is.
Roasted Barley: rinse off pearled barley to remove dust.
Caramel Malts: soak your un-crushed 2 row malt in 150 F water for about 1 hour. This takes a bit longer than regular mashing because the grains need extra time to temperature stabalize and rehydrate then crushed malt.
for light to medium roasted grains:
Spread about 1 lb of prepared grains over 2 half-sheet pans, and stick them in a 325-ish oven, preheated. For a light roast cook them about 20 minutes, light to medium, 40 minutes, and medium roast: 1 hour. The damp, wet caramel malt will take about an extra 15 minutes to cook, for it needs time to dry out. If your oven is too hot, usually more than 350 F, your grains will start to smoke, making the whole house smell like a toast factory, and usually setting off the fire alarms. Don't let the grain smoke!!! Get as close to 350 F as you can without smoking, specially for the caramel, as maltose sugars carmalize at 352 F (FLAVOR!) Use your spatula to stir the grains every 10-20 minutes, as the grains toward the edge of the pan will cook faster, and the idea is to get the whole batch to be close to the same "doneness".
Don't use the husk color of whole malt to determine doneness. You'll have to take a grain or two from oven and slit it up with your figure nail. Note the color of the inner endosperm (ha ha! I love that word) during roasting. It changes from white to cream to tan to redish to brown and finally black. Carmamel malts will get a bit mushy and hollowed during the mash, but there should be just enough inner grain to give you an idea. With pearled barley just use the outside color for "doneness".
For darker than medium roasted grains, you'll have to move outside. Plop 3-4 table spoons of grains in our handy pop-corn maker. Make sure the grains are all moving and rotating in the bottom of the machine. If the grain is not moving at a good pace, they'll take way longer to roast, will stick and burn, ruining your pop-corn maker. You'll have to pre-dry your caramel malts in the oven for 15-20 minutes before this procedure, as they'll stick like glue and burn. Roast your grains for 5-10 minutes each batch, and usually in about 40-45 minutes you'll have a pound of medium to dark roast grains. Here's the tricky part: your grains will lightly smoke during this process, specially with the whole malt, as a good portion of the grist will burn off. Don't let the grains smoke too much though, as this means the outside of the grains are burning, and you'll have charcoal on the outside and still light insides. To prevent this from happening, simply drizzle a few drops of water into the cooking chamber whenever you see smoke. The water will near instantly turn to steam, and immeadiatly stop the smoking, making the grain cook slower and more completely. This is especially true during the end of cooking. It's very easy to over cook the grains when making dark roast so keep watch of your grains! If the once moving grains start to slow down and stick to each other, pour out the grains into a metal sheet pan immediately. You cannot cook these grain further. They're as black as you'll be able to make 'em. When you dump the grains they will immediatly start smoking when they hit the fresh air (I don't know why). It's important that you cool the grain fast, as they'll burn and continue cooking. Stir and shuffle the pan to cool the grains off. (this is the same phenomina that happens with roasting coffee... youtube it)
Sorry for the long post. Thought the info may be helpful.