Very few researchers design their own BIBD's. That's a very specialised area of Combinitorial Mathematics. Most people select an appropriate design from a published catalogue. Or use a program to make a design for them which is not necessarily the most efficient.

I usually go to the website called DesignTheory.org, linked below, to find an appropriate t-design. There, you might find the following BIBD, with 8 items, presented in 14 blocks of 4, each item presented 7 times and each item compared with each other item 3 times.

Block A B C D

1  0 1 2 3

2  0 1 2 4

3  0 1 5 6

4  0 2 5 7

5  0 3 4 5

6  0 3 6 7

7  0 4 6 7

8  1 2 6 7

9  1 3 4 6

10 1 3 5 7

11 1 4 5 7

12 2 3 4 7

13 2 3 5 6

14 2 4 5 6

So you would randomly allocate respondents to one of the 14 blocks, or, better still, assuming that respondents come in to your lab at a more or less random order, you would systematically allocate respondents to the next one of the 14 blocks to ensure that all blocks were about evenly included.

http://www.maths.qmul.ac.uk/~leonard/designtheory.org/database/t-designs/