Recently I worked with one of my customers on deciding how to streamline end user communication, and we of course started talking about the Maintenance window in SharePoint (See my blog for more information).
We then got into conversations about how it worked and they directed my attention to the fact that you could not edit the message delivered to end-users, my response was that it did provide a custom maintenance link that would send you to a site where you can post any information you want (Helpdesk info, Change Management info, etc). I also did some more digging and found that they could in fact create a custom maintenance window with any message they want you can find it here
The first image shows you what the custom screen would look like and the second shows you what the OOB feature looks like.
The custom solution (Again you can find it here) as it is when you download it allows you to change the message delivered to the end-user, and works against a single Site Collection, this then lead to cost discussions. Since you would need to implement the code using your best practices, and any other color changes or functionality changes you deem necessary. While I'm not against customizations it is more expensive then OOB and you need to decide if it is worth it for your enterprise, in this case I recommended the OOB feature as I think it delivers the needed message and has a very low cost to use.
In the end you need to do what is best for your enterprise and your users, just make sure you look at all angles.