I am writing to consult about my agreement (new house)

I am writing to consult about my agreement with home builder (new house). My wife and I signed the agreement on Oct 6 (to be more precise we signed the first version of agreement a few day earlier but the builder asked us to re-sign a new agreement because there were several mistakes made in the first one, at that time I wrote a cheque for $10,000). The builder signed the agreement on Oct 7. Since it was signed I started arranging financing which include transferring money from overseas. Due to some problems I failed to transfer necessary $10,000 and the cheque was returned to the builder unpaid. 

I got to know about that problem on Friday, Oct 15. As the builder doesn't work on Fridays, on Saturday, Oct 16, I informed them that the cheque would be retuned and that I had some difficulties with financing. Since then I have been negotiating with the builder simultaneously trying to sort out my problems. 

So, two decisions are possible. 
If I sort out my matters and provide proper financing soon It would be OK. 
But if I get a firm understanding that I won't be able to guarantee the financing I will have to quite (terminate) the Agreement. 

Could you please make it clear for me what is the legal procedure of terminating the agreement on this stage and if there is any fees. Do the fees depend on the date of termination?

They say that they will accept the delay payments.

The agreement was signed. We missed the conditional period. There was no payments made (my cheque was returned).
Should we give them the letter of termination?
From the practice, what are the worst possible consequences for us if give the letter of termination just 7 woking days after the conditional period?


Thanks, Mike