Well there are SOOOOOOOO many ways to do the front walls and I haven't finalised how I will but i will let you know my considerations so far.
The first is that now we have decided on the tunnel height and depth we need to decide on how to get rid of the smoke from the fire, and thats basically IT, everything you do at the front is smoke rid and prevention of heat loss.
90% of things i have seen have an oven spacethen it drops down at the front so that the heat is kept in the oven but then it opens up again generally with a chimney that "draws" the smoke away. The process of wind passing over the chimney top creates the "pull" to "draw" the smoke away.
Some ovens don't have a chimney and let the smoke come out the front, i find this creates a dirty front to your oven , if you create a chimney you can do some nice brickwork at the front and it should not degrade over time.
In a nutshell, you need a front that is smaller then the tunnell and then goes back out to wide again so you keep the heat but get rid of the smoke.
