I'm in the midst of saving for our house deposit with my wife.
The big realisation we had when we got to a point of looking seriously at houses is just how much extra expense you need to fork out on top.
You want to get the most thorough, detailed, and reputable survey possible. This is absolutely imperative. You don't want to miss out on any details with regards to the biggest purchase you will ever make. From investigations we have made, budget £1000-£1250 for this. There are huge horror stories from people who didnt check everything.
You have stamp duty to pay. Depending on how much you are thinking to spend, this might be nothing, all the way up to several thousand pounds. Its a % of the purchase price that varies based on the band the house falls into.
Then you have the solicitors fees. I've had friends buy places where they have literally had to drag the solicitor kicking and screaming the whole way, chasing paperwork on a near daily basis. Moving house is properly stressful, invest wisely. Budget another £1250-1500 here.
The list does go on - including removals, new TV/Phone/Insurance/etc policies - but its a decent chunk of cash that you don't end up having a lot to show for at the end of it.
The other thing we found is that several houses we went to look at would need some money spent on (either because of something simple like a lack of plug sockets, all the way up to the property benefiting from a new central heating and hot water system). Personally, i'd want this done before moving in. Depending on the amount of work, along with some quick painting afterwards, consider extending the rental term in your current property for an extra few months whilst you get all the work done. That way, you move in with it all ready to go. Much nicer.
We want to put down a minimum of 20% to get the lower interest rates on the mortgage, so with that and all other associated costs, it is a significant amount of borderline aggressive saving that we are currently doing. We agreed we didn't want to survive on mouldy bread and water between now and then, so just be sensible to make the most of saving cash.
If you aren't good with money, sit down and work out just what you spend your cash on, do a budget plan, and take out cash instead of spending on cards for a few weeks to see just how fast buying a cup of coffee at lunchtime, or not taking in your own lunch eats into budgets.
Importantly, set savings to go out at the beginning of the month just like any other bill. Be realistic at what you set to go out else you will just end up clawing it back, but also consider 'sweep' facilities to push over unspent money each month.