This runbook sizing an Elastic pool set Maximum DTUs utilized by all databases in the pool  . And set Maximum storage bytes utilized by all databases in the Pool. You can look up the available characteristics and tiers on https://docs.microsoft.com/en-us/azure/sql-database/sql-database-elastic-pool  

This runbook takes the following parameters:

 
ResouceGroupName: The name of the resource group that the SQL server is part of.

ServerName: The SQL server name.

ElasticPoolName: Specifies the name of the elastic pool.

Dtu: Specifies the total number of shared DTUs for the elastic pool. The default values for different editions are as follows: – Basic. 100 DTUs

DatabaseDtuMin: Specifies the minimum number of DTUs that the elastic pool guarantees to all the databases in the pool. The default value is zero (0).

DatabaseDtuMax: Specifies the maximum number of DTUs that any single database in the pool can consume. The default values for different editions are as follows: – Basic. 5 DTUs

Edition: Specifies the edition of the Azure SQL Database for the elastic pool. You cannot change the edition. The acceptable values for this parameter are:- None

SubscriptionID: An optional subscription ID if you want to work against an Azure subscription. The default is subscription is selected if not set.   

Download link: https://gallery.technet.microsoft.com/scriptcenter/Sizing-an-Elastic-Pool-c92d6ec4

How to Creating or importing a runbook in Azure Automation

How to scheduling a runbook