General manager Sam Presti announced the deals Friday. Terms were not disclosed.
Oklahoma City took Adams, a center, with the 12th overall selection in last month's draft.
Adams, the first player from New Zealand to be taken in the first round, averaged 7.2 points, 6.3 rebounds and 2.0 blocks during his first and only season at Pittsburgh.
Guard-forward Roberson, taken with the 26th pick overall, averaged 9.6 points, 10.0 rebounds and 1.4 blocks during this three-year career at Colorado.
Oklahoma City acquired the rights to Roberson from the Golden State Warriors on draft night.