The proportions are really important - particularly with a big guy, you need to make the kilt long enough so it doesn't look wider than it is long - even if it isn't, it can give that impression.

You could try having him hold a piece of material at different heights around his waist level - maybe with a belt if he is going to wear a belt with the kilt, and fold it to different lengths so you can see what looks best. If it looks right from the front then its most likely going to be OK the rest of the way round.

I'd also say try your hand at knitting the kilt hose - so you can make some which are fairly chunky, as fine ones are going to look a bit sparce on a big man.

It can be a little difficult finding a fabric right for making a kilt. You don't want it too thin, nor too stiff, so many dressmaking and upholstery fabrics are out. It should be fairly heavy but soft enough to swing fluidly as that will also help when shaping the pleats into the waist at the back. It also needs to be non fluffy, or be pressable down into a non fluffy state, so that the multiple folds do not add too much bulk to the hips. You can cut out the back of the pleats to reduce the thickness, but it the fabric is dense to start off with it helps.

Of course a high quality all wool twill is going to be the easiest to pleat and sew, but it can be quite expensive. If you have more time than money you can always make a trial kilt in an unsuitable fabric just so you know you can work out the pleats and how to shape the aprons, then have the garment to try on at the end and see if it looks right. Something like a poly cotton sheet or duvet cover will be fine for that, and an old one which is softer better than a new one.

You might find that you need to twist the aprons and the pleats so as to get them to look right.

At the edge of the aprons there are a couple of large pleats which go under the aprons and give enough hem so that the aprons are not pulled apart when climbing up stairs for instance. The visible edges of the aprons are shaped with a slight flare - the under apron is only shaped one side as the other edge is hidden. All that means that you can make adjustments so that when the pleats are sorted out and neatly fitted into the waist at the back the top of the aprons proceed on around the waist so the aprons do not wrinkle or stick out. The kilt should fall as straight as possible from the hips front and back.

I am sorry if that seems rather daunting - but once you can get some material into folds and have it tried on it should be easy to see what needs to be done.

I make all my kilts and after a few false starts it became simply a matter of getting the folds in the right place and then sewing them accurately so they did not twist. Thats another thing - you need to sew on the grain of the fabric. If the fabric is twisted by being rolled wrongly, you need to straighten it before starting to sew (ask me how I know?)