Nepal is an exotic and exciting place for shopping - particularly in Kathmandu.
Kathmandu, in particular has an excellent variety of shops offering a whole range of goods, from traditional Nepalese arts and crafts like handmade clothes, carpets,pashminas, pottery, jewellery, religious Thankas and paintings along with antiques to all the modern electronic gadgets found in the more developed areas of the world. 
Carpets weaving is a long established traditional business in Nepal and it is considered to be a traditional art in this country.A traditional Nepali carpet is approximately 100 cm by 180 cm. They are usually dyed with vegetable dyes in pastel shadesin the past many depicted dragon and Tibetan Buddhist symbols but nowadays there are many different patterns to choose from. If you have the time you can design your own carpet and it will be made for you.A great place for carpet shopping is the Tibetan Refugee Camp Jawlakhel, Patan.
For pottery,Bhaktapur a lovely old traditional town some 20 kms from Kathmandu is a good place to visit as it hosts Nepal's famous pottery market.You are also able to watch the potters at work as they sit in areas to the side of the market to work.
If you are shopping for jewellery ,Kathmandu is a good place to start the city has hundreds if not thousands of  jewellery makers and shops. If you want to have a personal design made this is often possible– and the costs are extremely reasonable.
Please note when shopping that most sellers will expect you to bargain with them. However, there are shops nowadays in Nepal which are targeted specifically at tourism where many of the prices are fixed.

If you are buying antiques in Nepal?
You need to get special permission from the Department of Archaeology to take the antiques out of the country. Customs in Nepal are extremely thorough when it comes to inspecting the baggage of those leaving the country.  For this reason, it is essential that you get receipts for any items when shopping which appear to be antique. Ensure not to buy anything when you are shopping which looks as though it is a black market antiquity as this could put you in a very difficult position if you are caught with the item in your baggage.