Custom Website VS Drupal/Joomla/Wordpress [closed]

It's hard to say. It depends on your experience level and the time you have to spend on the project. I can't say one way or another, but I can recommend a few things if you do it from scratch.

Use a template engine, such as Smarty, so you only have to create a few 'real' pages. Their syntax is a lot less bulky than PHP.

Stick with OOP PHP when you can, especially if you are doing a lot of repeat queries. I use my own PDO class with my other classes, and it's much easier to manage.

Spend some time figuring out exactly what you want for you database structure and then check out using some UML diagrams to make it easier to visualize. That'll save you a lot of time.

Use some HTML Framework, like Bootstrap or Foundation 4. They offer great platforms for you to start with decent looking website templates.

Again, depending on the size, a CMS may be better and they offer thousands of plugins, but you are confined to the features that they have to offer. On the other hand, custom PHP will take significantly longer, but you can definitely customize to what you need. I've done it both ways, so I won't recommend one specifically. I think it will just depend on how large it really is. Also, keep in mind that if you bring new developers on to your project, you will have to explain all the inner workings of your project, so that may be a deciding factor as well.

If the site is going to be that big, then custom PHP will take a very long time. Not only will you have to write everything, but then the extensive testing + bug fixes will also be extremely time consuming. However if you do have the time for it, providing you developed it using good coding standards, the loading speeds would be faster than using a CMS and you would of course have more flexibility.

On the other hand (and I'm not going to recommend a CMS as everyone has their own opinions), using a CMS will save you an major amount of time and will of course provide you with a stable developing environment and framework to work with. Not to mention you have thousands of extensions for each that are available to use, which again, saves a lot of dev time.

In the end, the choice is entirely up to you. If it were me, I would decide based on the deadline.

Hope this helps