Templates
It is best practice to use Infrastructure as Code (IaC) templates to deploy FortiGates & GWLB in AWS as there are quite a bit of components that make up the entire solution. These can be used to deploy a new VPC. You can also integrate with a new or existing Transit Gateway as well.
Reference the CloudFormation and Terraform templates in the Github repos below and reference the quick start guides for how to use these for a deployment.
Note
You will need administrator privileges to run these templates as they are creating IAM roles, policies, and other resources that are required for the solution and automating deployment.
fortigate-aws-gwlb-cloudformation
fortigate-aws-gwlb-terraform