A lot of questions need answers before anyone can even start to make a recommendation
How much money are you willing to spend ?
Do you want 24 hr monitoring , or only while the office is open ?
Are you looking for real time monitoring , or just recording the video ?
On site monitoring /recording/,or off site ?
If you are recording , do you have a secure location for the recorder ?
How large of an area, and what shape area , do you want covered ?
Do you want both interior and exterior coverage ?
How good of a video quality do you want ?
That should be enough to get started