While a regular size twin bed may be perfect for a child or for smaller adults, an extra long twin bed frame can accommodate larger adults or tall teenagers much more comfortably. Choosing the best one starts with determining how much space you have available in your room, as well as your budget for purchase and your aesthetic desires for the unit. An extra long twin bed frame can be made from wood, metal, or even composite materials, so you will need to do a bit of research into each type to find the one that will suit your needs the best.
Understand that an extra long twin bed frame will require an extra long mattress as well, so if you do not already have one, you will need to purchase one when you purchase the frame. This can add to the cost of the bed, unless you find a combo deal that includes both the frame and the mattress. Some frames will also require you to use a box spring, though others do not; an extra long twin bed frame that does not use a box spring can save you money by eliminating the purchase of a box spring. The dimensions of the box spring and mattress should match the dimensions of the frame.
When choosing frame materials, think about aesthetics, durability, and price. If you choose a wood frame, you have two general choices: hardwoods and softwoods. Hardwoods will be more expensive because they are naturally durable and strong, not to mention beautiful; softwoods tend to be less expensive but also more susceptible to damage such as warping, cracking, or splitting. Softwoods are usually fairly attractive as well, though it will probably be necessary to stain or otherwise seal the wood if the extra long twin bed frame has not been sealed or painted at the time of purchase.
Of course, the least expensive option is a steel extra long twin bed frame. These units may even be adjustable, though they will also require some assembly at the time of purchase. Such frames are usually mounted on sliders and/or casters that make the frame fairly easy to move, though these casters and sliders can damage a wood floor. Such frames are not always the most stable, nor are they the most attractive units, but for value and long-term durability, it's hard to beat the value and strength of steel frames.