The room where you record your voice is the most important place to spend your studio budget.
Recordings must not have any external noise on them - apart from your lovely voice! Some external noises can include; Computer fans, hum in your cables, birds or insects from outside, other residents of your house, traffic noise, aircraft, and air conditioner noise just to name a few of the most common. To prevent this kind of noise, you either need to put distance between you and the noise (i.e have a sleep out or cabin to record in), or put some 'mass' or air gap between you and the noise - such as using heavy sound proof wall linings, having double skinned walls, or being somewhere really dense - such as underground!
The other noise we want to avoid is reverb, or room ambiance where your voice goes out from your mouth and is reflected of the walls ceiling, floor, glass, tiles, mirrors and every other surface - resulting in an echo. To deal with this kind of noise we need to use 'sound treatment' material with very low sound reflectivity so that instead of reflecting the sound the walls and floor absorb the sound and it never gets back to the mic.
When considering layout and treatment of your room you have two options;
a) Build a sound-proof, treated booth in a corner of your office, and have a mic and screen (or lectern) in that small room to record and read from (see top right picture)
b) Treat your entire office space, record audio at your desk and try to keep noise to an absolute minimum (see bottom left picture)
With option 'a' you can purchase a kit-set booth, such as Whisper room, or ISOVOX, or Vocalbooth.com (there are plenty out there) or build some of your own walls, put in a window, add some treatment. Then you can load up scripts on a screen or print them out to read - set up a mic in the booth and start recording your voice tracks. Remember to leave a hole for your mic, headphones and power! The tricky thing with this option is fresh air. Those who really go all out build a complex system of sound proofed ducts (Called a plenum chamber) to allow silent, passive ventilation.
My preferred option is 'b' because you can do auditions so easily while sitting at your desk, and you have plenty of fresh air! If you need to record something you just hit record and start talking - it's all set up and the script is already in front of you! The down side of this approach is that computers, air conditioning, and other household members all make noise and make it onto your recordings, so you'll need to be extra cautious when finding the location and designing the space
My recording space (pictured to the right) has sound treatment on 4 sides, carpet on one and is open only on one side of the cube. Using a mic that rejects noise from directly behind it, you can effectively mask any sound coming from that sixth wall space and have a remarkably dead sound, whilst still feeling like you are working in a small office. The cabin is detached from any other buildings so there's no other human noise. My computer is a passive laptop which makes almost no sound and sits behind the mic. The only sounds that make it through are road noise (there is a country road about 20m away, with 10-20 cars per day) and when it rains heavily or the cicadas are out in summer. Then I have to add other methods of sound proofing!