There's a book out there called "your money or your life" or some such title that basically says that you should consider your free time costing you as much as what you make on an hourly basis. Therefore, if you can pay someone $7/hour to mow your lawn and it would cost you (on an hourly basis) $20/hour to do it yourself, you are better off paying someone to mow your lawn while you go and do whatever you like for that time period.

All of this is to say: if you like sewing/cutting/fitting etc. to make a kilt...go for it! If, on the other hand, you would rather be out biking/hiking/skiing, then you should just buy a kilt from a good kilt maker and be done with it.