As others have suggested get the hario cold brewer - dug mine out a couple weeks ago and make a batch every few days. I like it with ice, milk and ice or with tonic, ice and a slice of lime
I don't add sugar but I think as others have said it can be a little flat - some of the flavours don't sing as much as when brewed hot (others can explain that far better than me).
I use the hario for cold brewing. Have never found it bitter or flat but I tend to prefer lighter roasts, often natural process, that have floral/fruity/bright flavour profiles which I think suit cold brewing. Don't add milk or sugar but often have it over ice if it's really hot.
As others have suggested get the hario cold brewer - dug mine out a couple weeks ago and make a batch every few days. I like it with ice, milk and ice or with tonic, ice and a slice of lime