Compared to the rest of the Chicagoland market, the Northbrook submarket has lower rates, so you should have no trouble finding a great deal in this depreciated submarket.
In the last 90 days, 30 listings have been made available, which means listings most likley are leasing quickly. You'll want to be prepared to make an offer immediately. About 40% of the listings in the Northbrook are subleases, so you might be able to snag a great spot on a short term. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,790 sqft. Most buildings in this market are close to 4 stories. Most buildings in this region were built in 1980 and are Class A.