Custom made oil tank

Hi. Ive been asked on quite a few occasions,to have a go and make an oil tank.Ive looked on the internet at kits you can buy and weld up yourself,but I think I should be able to source all the materials and fittings myself to keep the cost down.
The style I was going to make was an upright one,with the filler cap angled slightly at the top.Full stainless steel,tig welded tube....4.5 inches wide and 8 inches high.The vent will be near the top,the feed tube will be at the bottom and the infeed tube will be a couple of inches from the top.
Does anyone know what size fittings would be used on something like this,and is it best to use those piggy tail style fittings so that the hose will grip them better.Just want to get this right first time.Thanks