type
  TMyCustomPanel = class(TAdvPanel)
  private
    FButton: TButton;
  public
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
    property Button: TButton read FButton;
  end;


{ TMyCustomPanel }

constructor TMyCustomPanel.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);

  FButton := TButton.Create(Self);
  FButton.Parent := Self;
  FButton.Top := 30;
  FButton.Left := 20;
  FButton.Caption := ''OK'';
end;

destructor TMyCustomPanel.Destroy;
begin
  FButton.Free;
  inherited;
end;

begin
  AdvPanelGroup1.PanelClass := TMyCustomPanel;
  AdvPanelGroup1.AddPanel;
end;