Poured Silo ??

No type of covering, just the bare concrete. My 20x72 Weaver Star silo roof has about a 2-12 pitch to it with about 3-4" i beams for reinforcement in the concrete. 

The poured silos with a poured roof are sealed silos with a bottom unloader like a Harvestore silo for silage and high moisture corn also.

Travel US 31 south of South Bend between the SR 4 exit and the Plymouth Parkway exit and look right .

The walls of most concrete silage towers were built with slip-form process... inner and outer rings as noted.   I have not SEEN those form ring setups, but my neighbor explained how his two concrete silos were built using those forms.  The inner ring form 'walked' up the interior of the silo as each successive lift was poured, and the inner ring's center area was basically a large 'wheel, with the center 'hub' being a pivot point for a gin-pole jib boom which reached over the edge to lift up concrete.   The 'spokes' of the wheel went to the forms below as 'flat' but above were inclined upward, to support the jib's pivot.

once the finished height was reached, the 'spokes' of the center were covered with plywood, and a THIN layer of concrete was poured, and rebar sections placed atop this concrete, with another thin layer placed atop the rebar.  Once the layers began to set up, they started pouring more concrete around the root (the wall tops), and steadily working upward to the jib boom pivot.  Then they allowed it to fully set up, the lifted up the (relatively small) concrete precast 'cap', and set it on the side of the lid in some convenient place, dismantled the jib, and lowered it's pieces down through the center hole, then slid the cap into place, and used the platform's jacks to lower the platform back down to the ground, disassemble it, and pass the framework and plywood out the access portal in the bottom.

I had a uncle in the 1940's that worked for the contractor that poured silo's for Stocks Mill in Hilsdale Michigan. They had elevators that brought the cement to a scaffolding and dumped it into wheelbarrows that was dumped by hand into the forms. The scaffolding was raised as the forms came up.  I was to young to remember much except the stories my uncle told. His stories were not technical as you might expect. My uncle was a wheelbarrow operator. (:^D