As a starting point, here's some info I posted on Brews & Views a few years back...maybe you can extrapolate from here...
I got the latest issue of New Brewer yesterday and there's an article on mastering altbier by none other than Dr. Frank Hebmuller, who is the brew master and executive brewer at Zum Uerige. Here's what he says...
Water can be relatively hard with a high carbonate level. This is pretty much what my water is like. Malt is based on well modified pils, with a bit of caramel malt and a bit of "chocolate roasted wheat malt". Dunno exactly what that is. Mash schedule has rests at 125, 144, 158, and 169 (mashout). Boil time is 60-70 min. Mittelfruh, Perle, or Spalt are the preferred hops. Aroma hop addition is about 25% of the total hop amount. Add aroma hops no earlier than 20 min. before flameout. OG is 1.044-1.052. Primary between 59-68F. Secondary at 50F. Then condition at 32F for 14 days. FG should be 1.008-1.014. 4.3-5.5% ABV Here's the recipe he gives for 5 gal. ....
5.9 lb. Pils malt
.15 lb. Caramel malt (e.g. Weyermann Caramunich)
1.34 oz. Chocolate Roasted malt (e.g. weyermann Carafa Spezial Type 1)
.7 oz. Hallertau Mittlefruh - 6.5% - 60 min.
.46 oz. Perele - 7.5% - 60 min.
1.11 oz. Spalt - 5% - 20 min.