There are several posts out there that talk about how to roast your own grain but I didn't see anything here about it yet, so I thought I'd share my experiences today while I roast a few different batches. I'm brewing a chili stout today, but it's a 1-gallon test batch, so I'll only be toasting 75 grams each time.
There's a lot of different times listed for different Lovibond ratings, but after my first batch this morning burned to a crisp I think it's safe to say that for most people, 150 C (300 F) will do the job. To get different L, just roast for different times.
Also, depending on whether or not you soak the grains for 15 minutes before roasting, you can get different flavors. Non-soaked grains will give you more toasty/roasty notes, while soaked grains give more caramel. Supposedly. We'll find out today.
My three different batches:
75 g maris otter, soaked for 15 minutes, roasted @ 150 C for 60 minutes (supposedly L60)
75 g maris otter, no soaking, roasted @ 150 C for 60 minutes (supposedly L120)
50 g flaked oats (not instant, but quick-cook. No soaking, roasted @ 150 C for 30 minutes. Doing this for just a bit of toast.