My advice is, look at lots of pictures, see what you do and don't like about other people's bikes. Set a realistic budget, figure about double the price of the kit. Be realistic about what you expect bike to do, and what upgrade parts you'll need . Think long and hard about your mechanical skills, and tool availability. If you must farm out welding, can the welder handle bicycle tubing ? Just like cost, build time can add up, welding, painting, fabricating all take time.
My favorite bike = H B C Huffy Beach Cruiser [ Cranbrook ]
48cc Grubee, Worksman wheels, Kevlar tires / thornproof tubes,
double centerstand, Pirate Cycle Hub, Sprocket, #415 chain
Domino throttle, caliper and coaster brakes, sound deadeners,
Triple sprung saddle.
Bike is smooth running, easy starting, downright fun.