How to calculate how much it will cost to do work on a property before you've bought it & moved in?

[Honey1975]

We are in two minds as to whether we should go ahead and buy a property. It needs updating throughout, basic decorating but we also would want to convert the garage to a playroom, amend the existing structure to create a new kitchen, block up a wall & knock down another.
We have taken a builder round who has given us an estimated cost for the work.
At some point it will need a need bathroom and could also do with a new, more secure front door.

We have the mortgage in place to purchase the property. We believe we have agreed a good price and the potential space it would give us would be great for our family.

We are trying to work out the finances to make sure we can afford to do this. We have rough estimates for the work but I'm worried that it's going to end up being substantially
more and we'll be stuck with things half finished!

Has anyone bought a property like this that could tell me how you worked out all the costs to be as accurate as possible before you were able to move in?

This is totally new to me & DH and on the one hand I'm excited at the prospect of having a lovely family home but am also nervous at the financial commitment as it will stretch us to our limits.
Greatful for any advice - we really need to make a decision on this now whether we go ahead or not.

I started a spreadsheet.
Went through each element of work required and gave a rough figure to each. (Based on previous knowledge)

Then I went and got rough quotes from people who were helpful enough to do it without seeing the job to know that I wasn't way off on my estimates.

Then when we got the keys we had people in straight away to price up officially.

So all the work that we planned to do has come in on budget or very close to.

Where we have spent extra is on the unknowns and emergencys that have happened that we weren't expecting.

Thanks dilapidated that's very helpful. How long did it take you to collate all the info?

We are at crunch time now as have had an offer on ours which means we could go ahead with the one we've offered on. I think we need to sit down tonight & cost it all up as best we can, maybe just by googling costs?

At the end of the day we can afford the house itself, it's just going to be a very tight budget to achieve everything we want to aswell!

I am scared basically of such a big financial commitment but if we were to find a similar size property which was already 'done' it would not be affordable for us.

It didn't take me too long.

With the agents floorplan I had rough sizes of rooms to work out flooring and kitchen.
Other things like decorating were more of a guess as it can vary so much.

Ok thank you. Have you had to find much more money to pay for the unexpecteds? This is what concerns me a bit. A builder has given us an estimate based on a 15 walk around the property - just hope he hasn't got it way wrong!😩