what i do;
i use boards/skis for lining (as mentioned above)
then i start with big blocks of snow(if the snow is right)
stack em in a pie-shape and fill up with smaller snowballs, or debris
then click into your skis and sidestep up and down the kicker while your friends throw on more snow on places that need to be filled up or made steeper
once it has the right form you sideslip down it several times and throw on a bit of salt, then let it set for 5 minutes (enough for you to hike up)
then click in your skis and speedcheck like you see in the movies, frenchfrie hockey stop near the lip; this smooths out any crap in the transition and on your takeoff
then when you judge it's good enough you can start sessioning it !
for jump building a takeoff for a rail in a park we line the jump with 3 wooden plates, shovel it full, then gradually layer by layer pour on some tapwater (we ski indoor so we have that within reach) so you end up with basically a solid block of ice for a takeoff, then we scrape and shape it into a jump :)
stays good for a day of sidejumpers molesting it :)
Belgium represent !
"The windows are vertical how am i going to poop on those?"-Killabees
"God isn't black, you fucking moron!"-Shibby
"I shit rainbows and sneeze glitter."-Arabian