I created 2 VPC's in the same region ( each vpc has - 2 public , 2 private subnets , 1 public and 1 private route table ) \
After that click on transit gateway

Enter Transit Gateway name and Description

UnCheck Default Route table association and Default route table propagationThis gives more control on routing 

A CIDR for the transit gateway must be provided . This must be unique to VPC CIDR of all the transit gateway attachment VPC's

Since in this case VPC CIDR start with 10 and 172 . I choose CIDR with 192

Click "Create transit gateway" to create 2nd Transit Gateway 

Disable route table association and propagation

Provide the CIDR for new transit gateway . Keep this unique to that of other transit gateway

Create Transit Gateway Attachments with each of the VPC's . 

Project1 VPC is attached to Transit Gateway 1 

Click "Create transit gateway attachment"

Click "tgw-0c6c9842be062ee49 (transit-gateway-region1)" ( choose the transit Gateway and type of attachment since we are attaching to VPC it's of type VPC

tgw-0c6c9842be062ee49 (transit-gateway-region1)

Select the VPC . for transit gateway 1 the vpc is project1-vpc . When selected we are prompted to selected subnets . Select atleast one subnet from each AZ . This enables transit gateway to reach the resources in that AZ 

Create Transit Gateway Attachments with each of the VPC's . 

Project2 VPC is attached to Transit Gateway 2

Amazon Web Services

Create Transit Gateway with Peering between Regions

Creating Peering Transit Gateway Attachments

Creating Transit Gateway Route Tables for each of the Attachments

Creating Route Table for project1 VPC attachment 

Creating Transit Gateway Route Table for project 2 VPC ( route table in another Transit Gateway ) 

Transit Gateway Route table for region1 transit gateway peering attachment 

Creating Transit Gateway Route Table for Transit gateway peering attachment of region2

Adding Routes for Transit gateway route table of region1 peering attachment

Route table association and Adding Routes for region2 peering transit gateway attachment

Updating Route Tables of both the VPC. Updating the route tables to route traffic to attachments

Create Transit Gateway with Peering between Regions

Creating Transit Gateways

Creating Transit Gateway Attachments