I would like to know if anyone knows who offer muti unit building insurance?

This would be a 3 unit brick apartment building

Call an independent agent & ask. You should be able to get a commercial fire policy on the building. If you are living in it you may be able to get a personal homeowners policy on it, some companies only write 1 or 2 families, some write up to 4 families. It just depends.
An independent agent will be able to give you the most options & has access to many companies.

Typically, insurance rates and coverage forms are filed by the various insurance companies that are licensed to do business in your State, and they vary from State to State.

The best thing to do is call a LOCAL independent agent. Just look in the phone book for the PIA or Big I (Trusted Choice) logos and you will find a professional licensed agent that will be able to help you solve your insurance problems, and give you rate comparisons of several different companies.

An independent insurance agent will normally have a dozen different companies and if he cannot help you, he should be networked with other local agents that can.

Most of the replies on this site say "go to this on-line carrier or that on-line carrier or that 1-800 number" but I'm sure that when you do, you may not find the answers that an independent agent can give you.

Good luck and I hope this helps

are you in australia?

if so, just type 'strata insurance' into a search engine and it should come up with companies that specifically handle multiple buildings on one lot.