Can anyone help me start building my own poweramp?

Go for it!!!

do you have any electronics experience?
How about hand tools and test equipment?

How loud do you listen...what kind of music...etc...

you need to figure out from your average SPL level at your listening distance and working backwards with your speaker sensitivity and figure out a ball park power figure. Then you would make a decision on the power delivery across load impedance: do you want the amp to "double down" all the way to 1 ohm (not really necessary btw, but alot of people seem to be hung up on that).

Going from the specs:Recommended Amp. Power:
Small size rooms: >25 watts
Medium size rooms: >65 watts
Large size rooms: -- watts
IEC Long Term Power Handling:
150 watts
Impedance, Nominal:
4 ohms
Impedance, (20-200 Hz):
3.4 - 19.3 ohms
Impedance, (200-20 kHz):
3.4 - 6.7 ohms
Impedance, Phase Shift (20-200 Hz):
-49° - +45°
Impedance, Phase Shift (200-20 kHz):
-4° - +18°

the lil 52 SE is actually more diffcult to drive than most of its kind. This implies a solid power supply and output devices of sufficient power dissipation (plus margin) are required to not sag under higher volumes, across the audio band.

An audio amplifer is basically a DC power supply that is modulated (amplified and controlled) by the low level input signal.

All the gain is (usually) done in the first 1 to 2 stages. The last stage is nothing more than a unity gain (gain of 1) buffer, to present a low AC impedance to the load.

For a conservative 50 watts I would recommend 2 complementary bipolar pairs per channel (4 total per ch: 2 each PNP, 2 ech NPN 150 watt Motorola/Toshiba types)

and about 30 volt "rails". You can find a well made toroid at www.toroid.com find one close to this secondary voltgae and about 500-600 VA rating. You can spec a multiple secondary job with extra windings for the lower power (but high voltage) input stuff.

You need about 30,000 uF per channel main filters, and then you can use smaller (220 uF) caps closer to the output devices.

1 bridge rectifer is all you really need. Spec a massive one though and bypass the diodes with hig quality poly caps.

The sky is the limit on the input/driver circuit. THis is THE critical part in ANY amplifer. Get this wrong and no matter how good the rest of the amp may be it might not even work to sounding horrible...

Get a book on amplifer basics online like Audio Power Amplifier Design Handbook, Fourth Edition (Paperback)
by Douglas Self (Author).
Excellent background and detailed viewpoint of what you relly need to understand to design an amp from scratch.

Of course you can get a kit and solder it all, but that is not designing it on your own. It will be challenging to get it right the first time and many iterations will be required. There is a ton of experience that goes into making a low noise, audiophile grade, hum free stable high power amp...

This is a VERY basic blurb...Get some books!!

Kenneth P from Denmark:
There are lots of diagrams in that book. I think it is a good read and presents a pretty thorough examination of the various stages of the power amp.
Randy Sloan used to publish kits of high quality DIY amps. I think if you dig enough you can find the schematics.

http://www.zusaudio.com/navigation/seal.htm

Also check out Nelson Pass DIY page for some really great articles and projects:

Amps
http://www.passdiy.com/amps.htm

Also there is much following for the kit based Lifeforce amplifiers from Hugh Dean if you want a very high quality amp with little else to do except get a nice case, buy a transformer and wire it up (i heard this amp and it is very good)

http://www.aksaonline.com/products_2_4.html

General:
Start off by reading the literature then forming ideas about what you think you want from an amp.

Get an idea about the case size (based on your other choices this size may change for increased heatsink area say.)
Sketch the mechanical layout of amp sections-

-transformers
-switches
-fuses
-rectifiers
-filter caps
-input circuitry
-approximate wiring
-output section
-input/output connections

once you nail down a design work from the schematic and build a BOM (bill of materials in excel or similiar) to keep your project sane. The BOM should contain every part in the amp, where you get it, how much it costs, who that vendor is, quantity needed...etc..

you will need to pay attention to:
how will you handle DC
how will you ensure stability (no oscillations)
how to protect against faults (dc, over current, thermal, input surges, you have to protect your speakers!!)

the devil is in the details but going through such an experience will give you much more respect for the makers of true high end gear. It is a long journey so be patient and keep an open mind.

If you happen to come across anyone from Dynaudio give them my regards. I love their speakers!