Cob: bedrock and cobbing

[sateague]

Greetings!
Am new to the list and have a few queries.  Firstly, bit ‘o background.  I
belong to the Society for Creative Anachronism (yes, those medieval
afficionados) and a few of us nut-bars (and I use that term with the utmost
affection)  are poised on the brink of an ambitious undertaking.  One of our
shire members has graciously allowed us several acres of land to experiment
with cob! Woo-hoo!  Biting off more than we can chew perhaps, we hope to
accomplish these things this season; stage one is an earthen oven.  Stage
two is a small 12 x12 structure.  Stage three is getting the foundation
ready for a rather large (final size to be determined) structure to be
completed the following season. The buildings will not require any modern
necessities (electricity, privies, etc.), we hope to make them as medieval
as possible.  Manpower will fluctuate between 4-10 persons/per workday
(hopefully more on the weekends).
The Location: Thunder Bay in northwestern Ontario - head of Lake Superior.
Summer season starts end of May (however, it's been known to snow in June,
yes, really!) and we generally get our first snow on Halloween night (it's
miserable for the kiddies).
Temperature: May-June 50F-80+F // July-August  72F-80+F //  Sept.-Oct
freezing-80+F
Rain: moderate        Humidity: dry heat       Winters: generally plenty of
snow, intermittent cold snaps lasting as long as 2 weeks.  However this
year, we had exactly the opposite weather. (Given a choice between the
greenhouse effect and snow, I'll take the snow, thank you)
The Site:  is rather ‘hill and dale', with lots of bedrock. We have 3 ponds,
a sandpit and plenty of natural vegetation  (ie.cat-tails, reeds, etc) and
locally available straw.  The property owners have a saw-mill
(wood-chips/sawdust), and a riding stable (dung) and the area is surrounded
by trees.  So far, so good..... my questions are:
1.  Can you build directly on a section of bedrock? In lieu of in-ground
foundation, building a  mortored stonewall of  2'+ high  along with  the
appropriate width and then cobbing?  We're fortunate enough not to have
earthquakes, and have never experienced a tornado.
2.  Drainage will be a problem on a level section, would a big berm be best?
(..try saying  that 3 times fast....) Even so, there might be seepage, so
would installing an earthen floor to enable wicking be a good idea?
3.  In the Cobber's Companion, the author mentions a German roofing
technique(coating reeds with clayslip, put a branch in the middle and fold
reeds over, attach wet...). Am most interested in this, has anyone tried it?
I've looked all over for more information, and I can't find any, arrgh!
4. Would it be possible to get a copy of the ‘Roman Cement' recipe from
someone?  Is the recipe a ‘modern' version  or the ‘real deal'?
Thanking you for your patience with an aspiring ‘mud-puppy',
Jackie