See this link. Working with shared folders.
IWHSInfo2 info = new WHSInfoClass();
IShareInfo2 share = info.CreateShare("SharedFolderName", "SharedFolderDescription", 0);
WHSUserPermission perm1 = new WHSUserPermission();
perm1.userName = "User1";
perm1.permission = WHSSharePermissions.WHS_SHARE_READ_ONLY;
WHSUserPermission perm2 = new WHSUserPermission();
perm2.userName = "User2";
perm2.permission = WHSSharePermissions.WHS_SHARE_READ_WRITE;
Array permsArray = Array.CreateInstance(typeof(WHSUserPermission), 2);
permsArray.SetValue(perm1, 0);
permsArray.SetValue(perm2, 1);
share.SetPermissions(permsArray);
Bye
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share