ASP.Net and IIS have a number of ways of handling this. App_Offline is one method, but it depends on if you need to have WAF running while showing the maintenance page?

Hi, we have added an option for a custom warning page regarding database changes after definition changes.

This feature is available in b 2116 and later:

https://www.nuget.org/packages/Relatude.Server/5.0.2116

Add this to appSettings in web.config:

<add key="WAF.DbChangeWarningPage" value="HtmlPage1.html" />