Custom UINavigationBar height working in iOS 7 and 8. To use, find your navigation bar reference and just setHeight:200 etc.

UINavigationBar+CustomHeight.h

//
//  UINavigationBar+CustomHeight.h
//
//  Copyright (c) 2014 Maciej Swic
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//  THE SOFTWARE.
//

#import <UIKit/UIKit.h>

@interface UINavigationBar (CustomHeight)

- (void)setHeight:(CGFloat)height;

@end

UINavigationBar+CustomHeight.m

//
//  UINavigationBar+CustomHeight.m
//
//  Copyright (c) 2014 Maciej Swic
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in
//  all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
//  THE SOFTWARE.
//

#import "UINavigationBar+CustomHeight.h"
#import "objc/runtime.h"

static char const *const heightKey = "Height";

@implementation UINavigationBar (CustomHeight)

- (void)setHeight:(CGFloat)height
{
    objc_setAssociatedObject(self, heightKey, @(height), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (NSNumber *)height
{
    return objc_getAssociatedObject(self, heightKey);
}

- (CGSize)sizeThatFits:(CGSize)size
{
    CGSize newSize;
    
    if (self.height) {
        newSize = CGSizeMake(self.superview.bounds.size.width, [self.height floatValue]);
    } else {
        newSize = [super sizeThatFits:size];
    }

    return newSize;
}

@end

Hi, I found out that there is a problem when you have your navigation controllers in storyboard. The main issue is that the width of your navigation bar is not stretched to whole width of screen. It looks like that method
newSize = [super sizeThatFits:size]; returns wrong width. I've added line of code that fixes this problem.
newSize.width = self.window.bounds.size.width; // just get the width from different source...

The whole size that fits method with small fix:

• (CGSize)sizeThatFits:(CGSize)size
  {
  CGSize newSize;

  if (self.height) {
  newSize = CGSizeMake(self.superview.bounds.size.width, [self.height floatValue]);
  } else {
  newSize = [super sizeThatFits:size];
  newSize.width = self.window.bounds.size.width;
  }

  return newSize;
  }

Enjoy :)