First off I also must ask why is it that big clouds are so important? is it just because it's cool? If it's what you must have to each it's own...I also enjoy blowing big clouds from time to time but I find a good flavor build is much more enjoyable than just filling the room with a fog of vapor.
Welcome to VU and I am glad you enjoy vaping! It's all about whatever keeps you off smokies so if it's time to step up than it's time to step up.
First, I would honestly recommend picking a good high wattage box mod...you can go the mech route if you like but with the high wattage regulated options that are available now it's a safer way to go starting out and you have much more flexibility with your coil building options as you have a regulated chipset driving a constant level of power to your atty as apposed to being at the mercy of the charge and and health of a battery with no other protection whatsoever. Next off you'll need to choose an atomizer. For the biggest clouds possible you're looking at a dripping atty with a lot of airflow. You need at least 1/8" minimum and I'd recommend more. Something like a Mutation X V3 or something along those lines with a ridiculous amount of airflow...
Next thing you need to know is battery safety....whether you go the regulated option or old fashioned mech you need good solid IMR or INR hybrid chemistry 18650 batteries with at least a minimum of a 20 amp "continuous drain" rating. Being newer to this you don't want to go of the "pulse rating" as the battery can only fire at that level of amp drain for a few seconds and it is a dangerous game of playing with it above the continuous drain limit. I have a thread in the "e-cigarette safety" section of an atty failing and a battery almost venting on me proving why you don't want to go above the continuous drain limit. Some good recommendations for batteries would be Samsung INR18650-20R's or their 25R counterparts, LG HE4's, Sony VTC4's, or AW's old 1600 mah 18650 or their new 2200 mah 20amp 18650 battery. The Efest and other's are ok as well, I just listed my prefered ones there.
Once you have the right mod, atty, and batteries you'll need to build a coil. There are many tutorials here and on youtube to get you started with it. The first thing you need to know is you do NOT need to build a super sub ohm coil to get big clouds. That is a myth. I have a patriot with an Infinity pyrex glass cap with 1/8" airholes that I can get just as big of clouds off of with a .7 dual coil build at 25-30 watts as I can with my Mutation X V2 built with a single parallel coil at .24 ohms on a mech with a fully charged battery. Clouds are made with a combination of coil build, proper airflow, the right juice, and the right amount of power supplied from the mod...any one of these alone won't give you the clouds you seek. It is all of these things that make up clouds. That being said...since you're new to building I would recommend getting some 26 gauge wire to start...wire is cheap so get some 24 and 28 as well. Don't start out with 20 and 22...until you learn the finer points of building it's just too low of resistance and is too easy to get into trouble with more than make what you want...oh I almost forgot...you need one of those little ohm's reader boxes and need to learn the basics of ohms law....here is a link to an ohm's law calculator and a coil building engine that will help you figure out you're coils.
http://thelocust.net/ohm/
http://www.steam-engine.org/coil.asp
Anyways...get some 26 gauge wire to start with...you want to start with a higher resistance just to be safe in the beginning till you get your feet wet and a little bit of a feel for building. If you're using a mech mod and a 20 amp continuous drain battery like I said, the lowest safe resistance you can build do to is .21 but I would stay above .25 to start with. Builds that low without the proper airflow can be quite uncomfortable if you're not used to it in the beginning and will take some getting used too inhaling that much vapor anyways. If you use a regulated box mod you can build as low as the device will allow but it's not nessecary and is better with those to build like at .5 or .6 anyways to take advantage of the devices range.
Start out wrapping a single coil of like 7 wraps and then since wire is cheap make a dual coil build of like 7 wraps and see what both meter out at with your ohms checker and see how they vape. Use this as a starting reference point to finding what you like...if the vape is too warm/cool...too much/too little vapor...etc.... get a 2.4 mm and a 3mm drill bit or a little bigger, I use a 3.2mm myself. Especially with lower gauges like 24 and lower you'll want to build coils with a 3 mm diameter bit or a little bigger so you can get enough cotton to wick it with that it doesn't dry out too fast. with 26 gauge you can use a smaller bit still because it's not as big of wire but I wouldn't personally go below the 2.4 mm diameter as I recommended in the beginning. Like I said, this is just to start out, once you get a feel for basic builds you can youtube all the crazy builds you want and go nuts.
Wicking is the most tricky part of the build. You want just enough cotton threw the coil that there is just a slight resistance pulling it threw. Too much cotton stuffed in will "choke" the coil and it won't feed properly and dry hit...and too little cotton and the wick will collapse inside the coil and again you'll get dry hits just because you're wick isn't hitting the whole coil and can't keep up. Cotton is cheap and this just takes practice...it's a finesse thing that can't really be explained better than that. You'll get it in time.
Lastly is E-liquid....the more VG in the liquid the more vapor but the less the flavor...plus the higher the wattage and the hotter the vape the more you "fry" the liquid and it will produce more clouds but you'll literally "cook" the flavor out of it if the vape is too hot. There are several good high and max vg juices out there but you'll want a 50/50 blend minimum to blow really good clouds.
There is so much more to tell but I have written too much anyways to start. Hope this helps and best of luck to you...I wouldn't impulse buy anything. I would shop around, find the lowest price, and ask around here about something and watch/read reviews on anything before you buy. Buying on impulse is a 50/50 shot of you'll love it or hate it....there's plenty of info on just about anything vape related if you look for it so take your time so you don't end up buying several things in a short period of time to get what you want like so many of us have before.
Happy Vaping and good luck!