Question regarding Expired domains

I'm looking for a new domain for a business. wont be 301-ing or anything.. i actually just want to build my site on and aged established domain with good metrics. I've found a couple of niche related domains that are "expiring" in a few days. All of them have good metrics.. however, i've read that once a domain expires/drops the metrics ie TF/DA/PA etc reset? is that true? or will i get the benefit of the domain's metrics for my website? Again.. i'll be buying the domain AFTER it expires. if that is the case and i do not benefit at all from the metrics, then, at what stage do i need to buy the domains so that i can keep the metrics? Cheers..

Ok.. i just read that i need to rebuild the old site on a dropped domain straight away in order to keep the metrics.. is it possible to keep the metrics without building the old site again? i'm gonna be using it as my main business site so i dont want somebody elses old site pages on my site .. it's in a similar niche so will google think i just did a major renovation on my site or something?