A few things you should consider before you get your self a spider, or any other animal. Is to find out how to build the terrarium and how big it need's to be. Here you can find a good start on how to do, but I suggest that you read more.

One of the first things you need to do is determent what kind of spiders you are dealing with (Which of the 3 groups of spiders it is tunnel/surfers/tree living spider). If it is a spider that need low or high air moisture. Of cause also how big it is and how big it gets.

When this is done you can start by creating the terrarium for the spider with the "perfect" of as close to it as you can get. I will give you some guidelines on how you can do it, but I will not go in to details with individual spiders.
We can start with the tunnel living spiders (Chilobrachys, Haplopelma, Lampropelma and some Selenocosmia's). This type of spider requires a "thick" layer of dirt "(compared to the other type of spiders) 25 - 30 cm (10 - 12"). The rest of the planning is more or less up to you, because the spider will not care as long as it can make tunnels. Other than that you will need to make sure the spiders has water and light. You can also add some plants if that is what you feel like. The terrarium does not need to be wry big as long as it can make tunnels in the ground.
The ground living spiders, don't need more than 10 - 15 cm dirt (4 - 6"), this kind it is a good idea to use some plants to help you keep the correct amount of air moisture. This kind of spiders can also dick but no way near as much as the tunnel living, you can help it making a "cave" by placing some wood somewhere in the cadge were it can live. Also here you should not be missing a small ball of water.
	If you go out and find some wood and other things for your spider's cadge, you may want to put it in the oven at 200� C for around 20 min to kill all the bug's and parasites in it. I would do this also if you get it in a shop, because you do not know if they have done it.
The terrarium for the ground living spider should be around could be 25x25x20 cm (10"x10"x82") but also up to 50x50x50 (20"x20"x20") depending on how big the spider is/becomes.
It is wry important to make sure that everything you put in the terrarium is secured and not able to flip over when the spider dick, because the spider don't deal with damage wry well.
Then we have tree spiders left, they live in the trees so here it would be good to have a "high" living space compared to the ground. This kind of spiders don't need a wry thick layer of dirt, because the make the cave in the tree's "in nature" You can be lucky to make it do that, but there is a big chance it might build it on the top of the ground behind some wood. For this kind you really need to have some plants, and some things the spider can crawl around on.