Finally I received missing Sapim Force spokes of length 254mm in black colour and built the new Big Dummy front wheel with lightweighted SON 20R dynohub and strong Spank Subrosa rim in chocolate colour. This time I took some pictures showing the building process which should pretty much follow Sheldon Browns guidelines with 3 crossings. Leading spokes run at inside at outermost crossing to maintain better tension at trailing spokes when braking hard with disk brakes.
The resulting wheel should be very strong. It has got 1197g of weight (including rim tape, without quickrelease axle). That appears quite ok for a durable disk brake dynohub wheel. The new front wheel will replace my current SON 28 / Spank Subrosa front wheel at the Big Dummy. The latter one will be installed at our winter MTB where it will replace an older Shimano dynohub wheel, making it easier to juggle lighting equipment between those cycles just in case. Also I can finally install my Shimano XT centerlock front disk rotor to the Big Dummy, replacing a cheap noname 6 bolt rotor. And last but not least, it will shave off another 200g of weight without introducing any compromise.