Well, first off, your lender should be in contact with your Realtor CONSTANTLY. They are linked, and will stay linked throughout the process, so communication between the two is VERY important.
Your maximum pre-approval is calculated using a formula called a "debt to income ratio". In essence, it is a ratio that describes the maximum in monthly payments you can have as a portion of your maximum monthly gross income..
So, very simply, if you have HOA and Mello-Roos costs, those are monthly costs that will take up a portion of your borrowing power...
For instance: Conventional loans are typically approved at about 45% max debt to income ratio.
If you make 10K per month, that means ALL of your debt (including your proposed new home Principal, Interest, Taxes, Insurance, HOA, Mello Roos, etc...) has to be under 45%, OR, in this case, 4500 dollars...
So, if you have 1500 dollars worth of credit card payments, car payments, and a loss on a rental property, that leaves you with 3,000 dollars TOTAL for your new home payment...
Obviously in this case, you can buy a lot more house if you DONT have HOA's and Mello Roos, or any additional payments, because more of that "bandwidth" is freed up for actual LOAN payments.
Many times we will have clients pre-approved for 500K on a HOME, but only 450K on a CONDO, because the 400 dollar HOA takes away from what would have otherwise been available "room" to increase their loan amount...
Any other questions or for a second opinion on rate/costs, I am available to help in any way that I can.