Fit is everything
While there's a lot to be said for the slimming effect of oversized and longline T-shirts on a portly build, the same cannot be said for baggy tailoring. Instead of amplifying your bulk with a suit that leaves "room to grow," opt instead for a jacket and pants that fit nice and close to the body. Not only will this reduce the appearance of bunching and tension in the fabric, it will also help you feel comfortable and look in tune with your shape, rather than fighting against it.
The above point leads us onto our next perfectly. It's a man with deep pockets that can afford to get his suit tailor-made from scratch. That said, there are plenty of suits available on the high street (and online, obviously) that can accommodate the big-boned, which can later be altered by a tailor to create the most flattering, streamlined silhouette possible.
Keep it simple
Classic, uncomplicated clothes are a big man's best bud. Sidestep the patterned suits trend, as heavily printed fabrics tend to exacerbate the appearance of lumps and bumps. Stick to classic cuts (nothing too skinny) and dark colors (navy and black are always a winner).
The finishing touches
A quick tip to ensure you're making your suit work as hard for you as possible is to keep a single button fastened at all times — this'll mean the fabric will sit close in against your widest point (the belly). The addition of a pocket square and/or a lapel pin is also a nice touch and serves again to draw the eye upwards away from an areas you're particularly conscious of.