A braggot is just a beer with honey added, or maybe a mead with wort added. There may be some technical definition saying that at least 50% of the sugar comes from the honey, but you can follow that or ignore it. If I was you, I'd do the following:
Figure out what flavor profile you are trying to achieve. Roast malts makes it sound like something towards a porter, or perhaps a stout or a brown ale.
Decide how strong you want it to be. Use a 50/50 mix of extract and honey to achieve the strength.
Take a look at extract with grain porter recipes (or stouts, or brown ales, etc) of about the same gravity as you want to brew and see how much specialty malt they use, and get an idea of hop varieties and amounts. Recognize that the honey will dry the beer out, and you might want to bump any crystal malts by maybe 25% to counteract that. Or you could decrease the bittering hops by a similar 25% to get balance that way.
Then just brew it treating the honey as if it was more extract, perhaps adding the honey in the last 10 minutes of the boil (remove the kettle from the flame while adding, and make sure it is dissolved and not sitting on the bottom of the kettle before you put the heat back on).
Good luck, and let everyone know how it turns out.