$validateUser = Validator::make(Input::all(), User::$rules);
$validateRole = Validator::make(Input::all(), Role::$rules);

if ($validateUser->fails() || $validateRole->fails()){
    $validationMessages = array_merge_recursive(
        $validateUser->messages()->toArray(),
        $validateRole->messages()->toArray()
    );
}

class CreateUserRequest extends Request {

    public function rules()
    {
        //
    }
}

class CreateRoleRequest extends Request {

    public function rules()
    {
        //
    }
}

public function store(CreateUserRequest $request, CreateRoleRequest $request2)
{
    //
}

<input type="text" name="user[name]" />
<!-- and later -->
<input type="text" name="role[name]" />

public function rules(){
    return [
        'role.name' => 'required'
    ];
}

$request->input('user'); // returns an array like ['name' => 'foo', 'other-user-field' => 'bar']
$request->input('role'); // returns an array like ['name' => 'baz', 'other-role-field' => 'boom']