What you also have to remember is commercial work is few and far between unless you can clean their windows differently...cheaper.....or can other something thats going to let you do the work you are never going to get it.
Firstly you need to contact the facilities manager and ask him if you can send some info.Then you could wait months until they contact you with a yes or no.Then if you do get it and you do the clean you could wait months again until your paid.
You can look at local council websites and authorities for tenders but most will ask you for 5million liabilty at least.
i do cleans for building contractors,race teams,schools,pubs and lots of managed flats most of these have taken years to get but if your in it for the haul youll be ok.
Ive quoted lots and lots private schools,factorys,nursing homes and never even had a call back...what you didnt have you wont miss move on to the next one.
Sometimes youll need luck youll be in the right place at the right time and someone will use you for their offices.And alot of work will only come by word of mouth you clean his windows and his mate has ashowroom that needs cleaning simple as.
These jobs take time to get and like i said you need something they dont allready have.
Certificates not really but you will definately need the following
Risk assesment
Method statement
Insurance certificate
some ask for your safety policy,manual handling record,equipment records,ppe the list goes on.