If you want to build a laptop from real Amiga-parts (read no Minimig,Natami etc) you would need to start with an A600-mobo as thats the only one small enough for a normal sized laptop.
Problem is it's also an extremly underpowered Amiga and once you start adding stuff like an accel (the ACA630 being the only reasonable option here) and an Indivision (also needed) a PCMCIA-card and Subway for connectivity you have not only a money problem but also one in space (this laptop would be very thick).
Driving this with batteries is also a no-go as the HW is neither low-power nor support any kind of powermanagment.
Or in short:
There is a reason why the PAWS used an A1200 and there is also a reason why it looks like it looks.
