Housing turtles
Most turtles are very good swimmers and need a large enclosure. The tank where we are going to keep the animals in can't be big enough. The small turtles we buy, will start growing fast, if we keep them Wright. Much depends on what kind of turtle you want to keep. The difference in size of some turtles is very big. Sliders, cooters, painted turtles and map turtles all resemble each other , and almost  require similar  care.  Sliders and cooters are hardy turtles and usually do well in captivity. However, they grow quite large, with some types approaching two feet, although most common species only grow to about 12 inches (30-40 cm)in length. Painted turtles are smaller and somewhat less hardy, while map turtles require the most attention to thrive. A wide variety of exotic turtles are intermittently available, such as leaf turtles, African mud turtles, and snake-necked turtles. Juvenile snappers and softshell turtles are also sold, but their large adult size and aggressive behavior make them unsuitable for all but the most dedicated turtle-keepers. Keeping a  animal like a painted turtle in a tank of 100x50x50( LxHxW)will be ok. Keeping a chelyndra Serpentina in such a small enclosure is asking for trouble. Oh yes they don't move very much and are so small when there young ..... These "standard" tanks are enough to hold a couple of small animimals, but don't overcrowd the tank. A tank of 150 x 50 x 60cm will do fine for medium sized turtles ( cooters and sliders). Again don't put to many animals in one tank. Don't put animals from different regions together, as they may need different kinds of housing and or food, lightning, heat...Putting decorations in a tank, like plastic plants,to have it look more natural isn't a good idea. Putting in plants...I should say yes, as long as you put in a turtle that doesn't eat them, or it will be very costly after a wile. Tanks decorated with natural plant life are highly decorative in combination with a piece of wood. Its also provides cover for the animals living in it. Plants contribute to the water quality by utilizing nitrates and giving of oxygen.
The aquarium should have a dry area (basking spot) so the animals can come out of the water to dry and lay in the sun or under a light bulb or other artificial heat source. A land area makes the aquarium look more attractive and is quite functional in addition. Basking sites are very beneficial to turtle, because shell is shedded and under natural sunlight parasites that maybe on the skin die. It is an absolute requirement if you intend to breed your turtles, as they will need an area in which to bury their eggs. With no access to a land area, a female turtle will retain her eggs as long as possible and then drop them into the water or on her basking area. The size and depth of the land area all depends  the type of turtle were going to keep. Also, some turtles are more terrestrial than others, so they will need a bigger land area than others.  The best way of making a land area is making one wile you are building the tank itself. When this is not possible and you already have a tank, then you can glue 2 stripes of glass to the sides of the tank, and put a removable piece of glass on top of them. 
Glue the strips so that they have a certain angle, so they come out of the water. This way the animals have a bigger swimming area. It's very useful that you can remove the glass for cleaning the tank, or if the turtle has to lay eggs. Instead of putting the glass plate back you can put a plastic tank in its place filled with sand. (picture)  On the glass you can lay a piece of rubber(i use car matts). Try to get natural rubber, because synthetic rubber smells. Don't use stones or gravel on the land area this will only damage the animals shell. Don't make a land area out of stones that are staked on each other. If the rocks aren't put firmly together, they could fall on the animal, injuring it or even break the tank. this also takes away a lot of swimming space.  Another way of building a land areas is a removable platform made out of glass (see baskin area)  Swimming against the stones could cause shell rot. Other decorations are not necessary, they will only leave the animal with less swimming space. Placing a thick piece of cork between the sides is another possibility.  Putting sand on the bottom is possible but takes more time to clean out the aquarium. Make sure that the tank is draft free, so no cold air can get into the aquarium. Make or buy a light hood that fits on top of the tank, so when the lights burn they give of heat and this heats the entire tank including the water. the temp. in the tank should be around 25°C, not all species have the same needs.(see lightning section). Try to include a hiding place in the tank. This can be made under the basking area. Just tape off all sides of the tank with cardboard or something else, so that the animals can swim under when it's disturbed, this can also serve as a sleeping place.

Constructing a tank by dkirkpatrick

One ViVarium Set up

Settin up your Turtle Tank