There is a book on my desk. There are some trees in my school. I also have an eraser in my pencil box. There are 20 chairs in my class. There is a blackboard in my school. There are some tall buildings in my school.

use

The noun after There be is the subject of the sentence and belongs to the inverted structure. The interrogative form puts auxiliary verbs and modal verbs such as be or will/have/can/must before there, while the negative form adds not directly after be or auxiliary verbs and modal verbs, so the sentence pattern "There be+ noun +place (time)" is often used to mean "what exists in a certain place or time".