So I am playing an artificer and my DM said I could build anything I wanted as long as I have the resources and can explain how I’m building it. I need help coming up with ideas and explanations of builds.

First as an artificer looking to build stuff start by revisiting the info on magical tinkering and on spellcasting - you need some tools of some sort (probably best are tinkering tools and thieving tools) then you are going to need some sorts of “parts” to build with. I recommend that you simply label things as “parts” and not as specific types of parts. N addition when buying equipment ballbearings, caltrops and string should be stocked up on for general as well as construction use. Then look for mundane things the party can use as the first things you start to build. They don’t have to be (& probably shouldn’t be) magical in nature other than perhaps what your magical tinkering can provide. You start the game with thieves tools tinkers tools and one artisans tools - I recommend woodworkers as wood will probably your most common resource available and can be used in a multitude of ways.if your going to learn other skills/tools in down time I would consider smiths, jewelers and leatherworkers skills/tools. That pretty well should cover the skills needed to make almost anything. What you make will determine the resources you need. What to build is the hardest part as that depends on your desires, game needs, party member needs.

Spend some time looking at the section on Tool Proficiencies in Xanathar's Guide to Everything (Pg 78).  It offers an expanded option on things you can do with your tools.  For example:

Smith's Tools
Smith's tools allow you to work metal, beating it to alter its shape, repair damage, or work raw ingots into useful items.
Components. Smith's tools include hammers, tongs, charcoal, rags, and a whetstone.
Arcana and History. Your expertise lends you additional insight when examining metal objects, such as weapons.
Investigation. You can spot clues and make deductions that others might overlook when an investigation involves armor, weapons, or other metalwork.
Repair. With access to your tools and an open flame hot enough to make metal pliable, you can restore 10 hit points to a damaged metal object for each hour of work.

Woodcarver's Tools
Woodcarver's tools allow you to craft intricate objects from wood, such as wooden tokens or arrows.
Components. Woodcarver's tools consist of a knife, a gouge, and a small saw.
Arcana, History. Your expertise lends you additional insight when you examine wooden objects, such as figurines or arrows.
Nature. Your knowledge of wooden objects gives you some added insight when you examine trees.
Repair. As part of a short rest, you can repair a single damaged wooden object.
Craft Arrows. As part of a short rest, you can craft up to five arrows. As part of a long rest, you can craft up to twenty. You must have enough wood on hand to produce them.

In addition, take a look at the section in Xanathar's for crafting items and magic items (Pg 128-129).   When your Artificer hits lvl 10, you can craft common and uncommon magic items with a quarter of the time and half the cost in gold.

While it's not entirely within your control talk to your DM about acquiring an All-Purpose Tool even if it's only a +1.  This item can transform into any kind of artisans tool and you have proficiency with that tool.  It'll give you the versatility to literally build anything you want and it'll will keep you from having to lug around a bunch of sets of artisan's tools.

One thing that my DM introduced for my Artificer character is a resource we just call "Sprocks". Rather than representing a specific object or device, a Sprock is just a generic term to describe useable tinkering supplies... so simple objects will cost one sprock, and the more it takes to get something to work the more sprocks it consumes. It gives you the leeway to not have to seek out every single piece of tinkering supplies... stuff like gears and springs can be handwaved as just sprocks.

Here's something I'm planning to make at some point... Get a Crossbow, a silk rope, a grappling hook, and a block and tackle... boom, now you've got a grappling gun. I don't have a homebrew ready for the rules on how something like that would work, but it's one of those things that I think most people will assume an Artificer has access to.

Ok thank you for All those ideas but what I was talking about  like Mechs giant machines like describing how I’m building them with tools like he would want me to say I spend hours hammering… like idk what to say lol

"I don't know as a player how to describe every step in the process, but my character would."

My artificer created maaaaaaany things and it was def only when I had the resources and valid enough description of how to achieve it (using existing class features, spells transcribed like a scroll on the object and manufacturing process). Naturally I still had to roll for it using the applicable Tool skill (not all tools were attributed to Intelligence either, thieves tools were Dexterity and Cooking Utensils were wisdom for example, but I did still have the expertise in them).

I play/played in a campaign where the DM has been playing since 2nd ed, so everything was hard and everything had risk. One of the first battles we had, I tried to feed the fighter (holding a sword and board) a healing potion as I was actively trying to play a purely party support build. Not only is it a strange, uncomfortable concept to imagine an adult adventurer trying to help another adult drink a vial of something while they're swinging a weapon against a nasty creature, but i was also given a DC check to do so (acrobatics or medicine check if I remember correctly). Naturally I failed the DC and the healing potion was shattered in the fray and subsequently wasted. I wasn't gonna risk that again, but eventually Id run out of spell slots and my reckless party mates will continue to need healing mid battle. So I made a syringe to inject a potion with, so I could use my action to administer a potion mid battle to subvert the DC and risk of losing potions.

The next town we went to I asked if I could use the forge and I had my long rest there. I forged the physical casing of the syringe using materials in the shop that I had already paid for and I specified I made it so it would fit many sizes of vials and potions with springs and latches and thing (like those Belkin phone phones for instance). Using the magical tinkering feature, I inscribed a combination of the scribed versions of the cure wounds and aid spells (like you'd find on scrolls or wizards books) on the inside casing and needle. I explained my ability to understand how to by pass the potions being imbibed by my infuse item feature, the fact that Im an alchemist and a doctor as a background. I then had to make the roll, which I added Flash of Genius, Guidance and my Tool proficiency too. Much to my "Save or Suck" DM's chagrin, I nailed this roll and the syringe became arguably my most used item from then on.

Just about anything you’re likely to want to make has some sort of real world analog - so you want to make a mech - basically a fighting robot. So you need joints ( both hinge type and rotating type) , muscles (look up how muscles work - basically a motor pulling a ratcheting line and pulley system), a solid frame to hang things on ( skeleton) and an armored shell (body) as well as some sorts of sensing systems ( magic eyes and ears). For pretty much anything you should be able to look up online what a modern analog has then recreate a simplified version and power it ( filling in the holes with “magic” and there you have the item.