container should be as big as child flutter code example

Example: flutter column min height screen sixe

import 'dart:math'; // for max function

// Add the following around your column
LayoutBuilder(
  builder: (BuildContext context, BoxConstraints constraints) {
    return SingleChildScrollView(
      child: ConstrainedBox(
        constraints: BoxConstraints.tightFor(height: max(500, constraints.maxHeight)),
        child: Column(), // your column
      ),
    );
  },
);