I'm in no way a professional seamstress, and the making of this dress wasn't used with any templates or copying a design. As far as I know this 100% original and of my own personal tastes and creativity (though I got the idea for the flower from a fellow creative online). With that said, I hope you enjoy. Let's get started making a dress for a Large-XL size Corgi :-D
Step 1: Create Pattern - Cut Out
Measure your dog, and create a pattern of the kind of dress you'd like to make.
Take the fabric (white T-shirt) and lay it out on the table. Take your dress patterns and pin them to the fabric. (you should have one front piece, back piece and a 'skirt' piece -I folded them in half to make it easier to keep things even. Don't cut along fold. Now you should have 3 pieces of white fabric cut out in to the shapes of your patterns.