Well lets see I really enjoy DIY stuff and didnt know anything about a sump set up, The guy at the LFS here had a sump setting in the back of his shop collecting dust it had been drilled full of holes and he said it wasnt doing him any good and he didnt want to mess with it, so he gave it to me.
I brought it home and cleaned it up sealed some of the holes and raised the 1st divider for more water in the first compartment,then in the second compartment I put about 3 inches of the gravel that is for plants eco complete, and planted about 20 lucky bamboo shoots in the second compartment,the water has to run thru the gravel from the top to the bottom to get to where the pump is, so the plants use alot of the waste.
I also have a crawdad in the first compartment that eats any big pieces of food or whatever may come down the pipe feeding the sump.
I have this setup hooked into a tank with 2 Oscars and they are pretty messy fish when it comes to eating.
for the over flow you can either drill a hole in the tank where you want the water level to be( had to put the hole there on this tank because the bttom had a label that said not to drill the bottom) also Ive noticed this set up doesnt make the gurgling sound the stand pipe does.
You can also use the type with a stand pipe which from what Ive seen is very common.
Te sump will only be about half full or so when the tank is full so if the pump should fail you will have room for the water coming out of the tank and not have an overflow. the water coming to the sump will be the same amount that your pump is puting in the tank, I use a one inch pipe to the sump so I am sure that the sump pump wont overfill the main tank.
Youll determine the size of the pump you need depending on the size of your tank and the amount of turn over you want.
Im still experimenting with this setup and have a few things I would like to try as soon as I get some hard number as to water quality and such. I can say this if I turn the sump off for about 4 days the water starts to get kinda dingy looking and when I turn it back on it will be as clear as if I had changed the water in about 5 or so days.
You can build a sump out of an aqaurium and some sheets of glass from a glass shop, and its realtively cheap, I just got a marine land lagoon setup and its pretty pricey.
There are a ton of DIY sump plans out there some are pretty extravagant ans some are simple just do a search for DIY aquarium sump and get some ideas, I built mine out of things I had.
I hope this helps you some, and good luck let me know how it turns out
Ron