As an obi, i.e. the belt that holds the kimono, is only a long square, this is relatively easy. The issue is knowing the exact how - and finding a suitable fabric with a suitable pattern...
The "standard" female obi used for the drum style tie (see Wearing a Kimono) is 3 metres long and 30cm wide. It consists of a decorated top fabric and undecorated lining with a stiff interlining. The first 110cm are completely undecorated. About 2m are folded in half lengthwise, the edges sewn together with a hidden seam, and the rest left open.
The Fabric is nowadays a firm synthetic with a slight lustre that mimicks heavy silk, used for both top fabric and lining. If you use a different fabric for the lininig, remember that it will be visible when the obi is worn, so the colour should be the same. A matching, but different colour is unsuitable. Decoration is, in cheaper commercial ware, woven in with coloured and gold/silver threads. Embroidery isn't suitable but for the wide end; everywhere else there will be too much rubbing of fabric against fabric.
Obi for young women and the very formal, very traditional kind are made of silk, decorated down the whole length, and not folded in half. This kind is most frequently seen on geisha (but alas, geisha are not frequently seen) and brides. Patterns range from uni jacquards through complicated coloured patterns to gold/silver thread, each more refined, delicate and dense than in the normal obi. There is, however, some leeway for creativity in both these kinds of obi. I have, for example, once seen a vintage obi painted with images of old European sail ships in something that resembled oil colour.
Obi worn with yukata are narrower (about 15cm for the whole length) and less decorated - without gold and silver -, sometimes even plain.
Obi for men are undecorated, 5-10cm wide, and shorter - just long enough to go round twice and be tied.