You should be as honest as possible. You should start write about the first time you met the contractor; while the project as on going and how you felt about the work they did when the project was completed. A few examples as what you can write about would be:
How was the communication between you and the contractor
Did the contractor present to you a detail breakdown of the cost/ scope of work
How did the contractor deal with change orders
Would you recommend the contractor to friends and family
Ask the contractor which site he uses the most so that you can write the review there. Hopefully its Buildzoom.
On buildzoom you can search for the name of the contractor and then right at the bottom of their profile there is usually a spot to write a review. Other websites have very similar procedures. If that all fails, your contractor should be able to send you a request for a review on whatever website they would like you to review them on.
very iodd I hadnot signed in found the company I wanted to review easily. Wrote review then needed to sign in. review gone and now site wont bring up the ocmpany