Adding a button to the bottom of a listview widget in flutter

change your buildlist function to include a column with the button and listview as children

Widget _buildList(BuildContext context, List<DocumentSnapshot> snapshot) {
    return Column(
        children:[
            Expanded(
            child: ListView(
                   padding: const EdgeInsets.only(top: 10.0),
                   children: snapshot.map((data) => _buildListItem(context, data)).toList(),
                   ),
            ),
            RaisedButton(
            // fill in required params
            )
         ])
}

To prevent the buttons being pushed above the keyboard;

return CustomScrollView(
  slivers: <Widget>[
    SliverToBoxAdapter(
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: <Widget>[
          // list items
        ],
      ),
    ),
    SliverFillRemaining(
      hasScrollBody: false,
      child: Row(
        crossAxisAlignment: CrossAxisAlignment.end,
        children: <Widget>[
          RaisedButton()
        ],
      ),
    )
  ],
);