An offline chart is not a custom indicator. In metatrader an offline chart is suppose to show you price info as a standard chart. Since it is like a standard chart you need to attach indicators to it.
Think that your renko is a normal chart, for a pair and a timeframe.
However, Renko is not a standard indicator. In mt4 to get Renko coders use a trick and create off line charts that are not designed for trading. Officially we do not support off line charts because you need to understand how they work, how they are created, how to update them and the downsize of using them.
However we have many clients that use Renko.
First learn to use the renko off line chart and understand how the bars are updated. Then attach indicators and see how they behave.
Also read this
viewtopic.php?f=11&t=1155&p=3429&hilit=renko#p3429