biscuit is a specialty malt. it's not really meant to be a main ingredient so much as something you fine tune with. if you want to play with biscuit i would recommend a low gravity mild with up to 1# of biscuit.
this malt is used to round out malty beers and make low gravity beers seem bigger. if you use it in an IPA use sparingly if at all. generally this stuff doesn't play well with higher gravity beers unless used in small quantities. i'd figure biscuit to be about 10% of any grist. maltsters say you can go up to 25% but i wouldn't go all in until you have first hand experience with it.
here's a brown ale that i cut down to a mild.
8# marris otter
8oz chocolate malt (english if you can get it)
mash in 1qt/lb of strike water @ 150F for 90 minutes. boil for 60 minutes
ferment with any well attenuating english strain. i use wlp007 (whitbread dry). you could probably use notty for simplicity. also, you can use any english hop or other low AA hop. that's why i put the AA content in.
In some 5 gallon batches (ok, well, one), 1 pound of biscuit malt is ok. But for the rest, don't go over more than about .75 pound of biscuit malt in a 5 gallon batch if you want a drinkable beer in the end. It's great in small amounts. But like salt, a little bit goes a loooooooong way.