you can get better comments if y describe this house - sg ft per floor, where will u use devices, where u will place the router, etc.

3 levels... typically hard to do with just one router for wifi.

rm700 won't get u much; a super duper router that MAY do for u will cost 2-3 times that.

yr case is not new, many have posted, a lot of comments/suggestion given in many threads.

but i have yet to read one such case where the solution is affordable, simple and TS satisfied.

u definitely can try the stock router they will give u when upgraded to 100 or higher.
but it is a fact wifi will not be good enough for even a std 2-storey house.

assuming a footprint of 1,000 sqft x 3 floors and router is at grd (level 1), it will ok for level 2 (except the far corners) but level 3 will be tough.
that is assuming u get a better router - the stock router won't do well even for level 2.
if u want level 3 coverage, either u use another router on level 2 as wifi extender which sucks becos 1/2 is already lost.
the best way is to lay a lan cable from router at grd level 1 to another router at level 2 or 3 to serve as access point (ap) for levels 2, 3.
this is a bit of trouble, but perhaps possible for yr new house under renovation?
also, try to get 100mbps at least to cope with the losses in yr tall house.
lastly, consider yr devices... old devices using in 2.4ghz will hv more difficulty; newer running on 5ghz can receive wifi better.

all that is said has been said many times over but there is no pinned thread for u to read.
i collected those threads and have added yr thread too!
you can see the discussion is repeated over and over:

Is it my router's problem ? (Tech Support)
https://forum.lowyat.net/topic/4618409/+20
Router sucks at wifi,homeplug any good?
https://forum.lowyat.net/topic/4594095/+20
Unifi standard download speed for 100mb
https://forum.lowyat.net/topic/4551990
2.4Ghz and 5Ghz connection, at different speed
https://forum.lowyat.net/topic/4195926
Need some advice on extending internet coverage, Condo,<2,000SqFt, thick walls
https://forum.lowyat.net/topic/4549805
Router replacement for unifi 100mbps, Router replacement
https://forum.lowyat.net/topic/4548858
Router recommendation, Need high gain and stable
https://forum.lowyat.net/topic/4538857
Best router for Maxis Fibre 30mbps, Best router for Maxis Fibre 30mbps (Home Networking)
https://forum.lowyat.net/topic/4547385
Router Recommendation
https://forum.lowyat.net/topic/4519582
wta unifi wifi extend, suggestion (Unifi)

This post has been edited by AVFAN: Jul 14 2018, 05:03 PM

not a router expert but i wud think yes - best router as main... connect 2 others via lan as AP's.