Extensive project, what car to aim for, civic, polo or other

[jay-c]

have studied the laws here in sweden so apparently if i modyfy a car i can have it registered as changed/rebuilt or amature built.. wich gives me free hands on all model years what car is best use for "extensive" mods
currently i think a Polo variant 1,9tdi, angle, possibly lower roofline and pull the rear end downwards like the prius/a6 sportback/5 series sportback. and some changes to the front end making it more aerodynamic, maybe other headlights (05 golf?)