Cold or hot smoker?
I've eaten lots of smoked fish in Scandinavia. It seems like a staple there.
How big and what fuel? You might consider just buying one as there are so many out there now it's hard to save any real money.
For a really a fast start pellet grills are gaining traction these days. They won't really run cold enough for cold smoking but you can drop a smoke generator in the fire chamber and cold smoke with one that way and they use the same pellets for fuel.